Based on the value of COMMON_ENABLE_OPENSTACK_INTEGRATION.

Installing requirements from the openstack role created role ordering
issues where openstack role had to run after the edxapp role so that the
required folders and the virtual environment are already created, BUT
edxapp migrations can also depend on the default file storage, which
will fail when using openstack storage if openstack requirements haven't
been installed yet.

Letting edxapp role install the requirements solves this problem.

While COMMON_OBJECT_STORE_LOG_SYNC and related variables are still
supported, this patch offers a finer grained control over tracking log
syncing.

Sometimes you want to host edX on openstack (and therefore need to run
the openstack role), but you still want to sync tracking logs to S3, so
it does not make sense to tie the choice of log sync store to the
presence of either aws or openstack role in the playbook.

The vhost role used to create directories required by the aws and
openstack roles based on the value of the VHOST_NAME variable, but that
turned out to be problematic (see https://github.com/edx/configuration/pull/3519).

Remove the VHOST_NAME variable and make each aws and openstack role
responsible for creating its own directories.

This adds two new variables to common_vars:

- COMMON_ENABLE_AWS_INTEGRATION
- COMMON_ENABLE_OPENSTACK_INTEGRATION

They are both set to False by default. When set to True, the
corresponding role (aws/openstack) will be automatically included in
edx_sandbox.yml and edx-stateless.yml playbooks.

We use to constrict our builds to PRs, similar to edx-platform

temporarily install google chrome stable

disable auto apt updates in xenial

Update credentials playbook

add fb and tw accounts to generic_env_config

Adds COMMON_EDXAPP_SETTINGS

* Default value is 'aws' (unchanged)
* Used by EDXAPP_SETTINGS, gitreload_env.DJANGO_SETTINGS, and demo_edxapp_settings variables

Conditionally adds postfix_queue role to edx_sandbox.yml

ECOM-5776

Ready for deploying Mongo 3.2

Feanil/ecom worker 16.04

Add a flag to easily turn on/off the logging.

Feanil/update aws cli

This is the credentials app. Not discovery.

Feanil/credentials 16.04

motd.tail support for Xenial

Add config for Zendesk custom fields