Various fixes to allows jenkins analytics to run analytics tasks on AWS resources

* Uses JENKINS_HOME=/edx/var/jenkins.  This addresses the pyinstrument
  re-install issue seen when JENKINS_HOME is a symlink.
* Installs libffi-dev and libpq-dev packages with analytics_jenkins playbook
* Adds an SSH Credential, which is passed as the MASTER_SSH_CREDENTIAL_ID
  parameter to the seed job.
* When the seed job is run, ignore unreferenced jobs, instead of deleting them.
  This allows you to run and re-run the seed job from Jenkins to update a
  particular analytics job, and untick the jobs you don't want to update.
* Lets <ANALYTICS_TASK>_EXTRA_VARS be a @path/to/file.yml

* Uses JENKINS_HOME=/edx/var/jenkins.  This addresses the pyinstrument
  re-install issue seen when JENKINS_HOME is a symlink.
* Installs libffi-dev and libpq-dev packages with analytics_jenkins playbook
* Adds an SSH Credential, which is passed as the MASTER_SSH_CREDENTIAL_ID
  parameter to the seed job.
* When the seed job is run, ignore unreferenced jobs, instead of deleting them.
  This allows you to run and re-run the seed job from Jenkins to update a
  particular analytics job, and untick the jobs you don't want to update.
* Lets <ANALYTICS_TASK>_EXTRA_VARS be a @path/to/file.yml

Prevent invalid display courseware in IE 10+ with high privacy settings

cleaning up my mistake

Added edxapp setting for AWS_S3_CUSTOM_DOMAIN

ECOM-4081

Updated go-agent documentation. Build examples are now correct.

Make CUSTOM_COURSES_EDX easily overridable

the go-server FQDN is now a variable passed to the playbook.

Replace nginx redirect method from rewrite to return for speeding up

Pull in hipchat 2.0.0.1 module and fix url encoding defect.

Add scripting to restore a GoCD server backup.

Install libmysqlclient-dev on go-agent docker so edx/configuration can be instaled

Disabling Boto/S3 querystring auth for edxapp

Add cluster tag as a part of abbey.py

The new code in the pipeline looks for the 'cluster' tag not the 'play' tag.  Add both for now,
we are working on a full replacement for abbey.py so this is just a shim until we can get to that.

This removes the querystring at the end of the URLs for our content uploaded to S3.

ECOM-4081

Added EDXAPP_LMS_ROOT_URL variable

  - restore a GoCD server backup
  - backup a GoCD server config via cron and bash script
go-server backup is performed using a separate backup user.
To change admin or backup user credentials, process is now to change
the sandbox-secure repo passwords and re-run ansible provisioning.
The passwords are written into go-server after the restore.

Add libffi to jenkins_worker and devstack

Fix typo from EDXAPP_COURSE_* to EDXAPP_COURSES_*

Cleanup playbook to be used in the continuous delivery pipeline

Continuous delivery playbook to create an AMI.

changing FOOTER_ORGANIZATION_IMAGE path

ECOM-3602

The EDXAPP_LMS_ROOT_URL has been added to simplify the addition of LMS-hosted URLs to IDA configurations.

ECOM-3602

Replace nginx redirect method from rewrite to return for speeding up

Fixed Docker issues for discovery service

Add marketing URL settings for course discovery.