Problem:

Intermittent "cb() never called!" errors on npm installs for platform.
This is likely due to a race condition on installing OS-specific bits that are built during time of install. When more than one compilation takes place at one time, this error can occur.

Workaround:

Detect the error and re-run the install. (When retrying, one or all of the bits have been compiled. So running it again just finishes the install.)

This change:
* gives us the flexibility of managing node from pull-request to pull-request. It'll be a huge lift to folks that want to test out node upgrades like @bjacobel or @andy-armstrong
* Sets us up for a port to Xenial, which will be accomplished in part by using nodeenv for managing the node environment. See a companion PR on the configuration repo for edxapp: edx/configuration#3444

This pull request does not:
* Attempt to solve any stability issues in builds related to node.
* Make node installs any faster
* Create any caching infrastructure to speed up node installs. They will be approximately as fast as they were before. Downloading the node bits build-to-build adds about 3 seconds, which is worth it for the added flexibility.

This reverts commit acf50c44.

This reverts commit ed80381b, reversing
changes made to 205cb8b3.

MA-2250

Available backends:

* django-oauth-toolkit (DOT)
* django-oauth2-provider (DOP)

* Use provided client ID to select backend for
  * AccessToken requests
  * third party auth-token exchange
* Create adapters to isolate library-dependent functionality
* Handle django-oauth-toolkit tokens in edX DRF authenticator class

MA-1998
MA-2000

edx-django-oauth2-provider is being mistaken for django-oauth2-provider. Making the filter less liberal ensures we properly uninstall django-oauth2-provider once.

ECOM-3647

Follow up to #11432. This value needs to be incremented to ensure the old package is uninstalled.

ECOM-3647

New package includes support for client credentials grant.

Sass compilation is no longer dependent on Ruby, so we are
removing its dependencies.

Please note that this is a squshed commit and the work of:
Symbolist, macdiesel, nedbat, doctoryes, muzaffaryousaf and muhammad-ammar

* Fix paver violations to stablize edx-lint update
* Parens, Line2Long
* Fix missing docstrings
* Fix PEP8 issues
* Address PR feedback (thanks @nedbat!)

This message is being shown to people who should not be deciding whether
to upgrade pip, so it is just confusing and alarming noise.

Before:

---> pavelib.prereqs.install_prereqs
---> pavelib.prereqs.install_ruby_prereqs
Ruby prereqs unchanged, skipping...
---> pavelib.prereqs.install_node_prereqs
Node prereqs unchanged, skipping...
---> pavelib.prereqs.install_python_prereqs
pip install -q --exists-action w -r requirements/edx/pre.txt
You are using pip version 6.0.8, however version 7.1.2 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
pip install -q --exists-action w -r requirements/edx/github.txt
You are using pip version 6.0.8, however version 7.1.2 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
Could not find a tag or branch '96e1922348bfe6d99201b9512a9ed946c87b7e0b', assuming commit.
Could not find a tag or branch 'b0686a76f1ce3532088c4aee6e76b9abe61cc808', assuming commit.
Could not find a tag or branch '88ec8a011e481918fdc9d2682d4017c835acd8be', assuming commit.

After:

---> pavelib.prereqs.install_prereqs
---> pavelib.prereqs.install_ruby_prereqs
Ruby prereqs unchanged, skipping...
---> pavelib.prereqs.install_node_prereqs
Node prereqs unchanged, skipping...
---> pavelib.prereqs.install_python_prereqs
pip install -q --disable-pip-version-check --exists-action w -r requirements/edx/pre.txt
pip install -q --disable-pip-version-check --exists-action w -r requirements/edx/github.txt
Could not find a tag or branch '96e1922348bfe6d99201b9512a9ed946c87b7e0b', assuming commit.
Could not find a tag or branch 'b0686a76f1ce3532088c4aee6e76b9abe61cc808', assuming commit.
Could not find a tag or branch '88ec8a011e481918fdc9d2682d4017c835acd8be', assuming commit.

This reverts commit 2ff0f636.

'distribute' is the ancestor of 'setuptools', and many packages require
setuptools to be installed.

Upgrade of MySQL-python from 1.2.4 to 1.2.5 is required because of an
incompatibility with setuptools>0.7.

add script to upload/download pip cache directories from S3

update all-tests.sh to use pip-download-cache from S3

update pip-accel to version 0.22

If paver is being run by a user that is not the same as the user
that installed npm on the guest machine, then paver install_prereqs fails
with the following error:

  ---> pavelib.prereqs.install_node_prereqs
  npm config set registry http://registry.npmjs.org/
  npm ERR! Error: EPERM, chown '/home/jenkins/.npmrc'
  npm ERR!  { [Error: EPERM, chown '/home/jenkins/.npmrc'] errno: 50, code: 'EPERM', path: '/home/jenkins/.npmrc' }
  npm ERR!
  npm ERR! Please try running this command again as root/Administrator.

  npm ERR! System Linux 3.2.0-23-generic
  npm ERR! command "/usr/bin/node" "/usr/bin/npm" "config" "set" "registry" "http://registry.npmjs.org/"
  npm ERR! cwd /home/jenkins/shallow-clone
  npm ERR! node -v v0.10.30
  npm ERR! npm -v 1.4.21
  npm ERR! path /home/jenkins/.npmrc
  npm ERR! code EPERM
  npm ERR! errno 50
  npm ERR! stack Error: EPERM, chown '/home/jenkins/.npmrc'
  npm ERR!
  npm ERR! Additional logging details can be found in:
  npm ERR!     /home/jenkins/shallow-clone/npm-debug.log
  npm ERR! not ok code 0

  Captured Task Output:
  ---------------------

  ---> pavelib.prereqs.install_prereqs
  ---> pavelib.prereqs.install_ruby_prereqs
  ---> pavelib.prereqs.install_node_prereqs
  npm config set registry http://registry.npmjs.org/

  Build failed running pavelib.prereqs.install_prereqs: Subprocess return code: 50

This change is a workaround. It will first see if the value is set. In the case
that is it not set, it will attempt to set it. (It will then fail; however,
re-running the task will subsequently be successful.)