Merge pull request #856 from edx/feanil/slow_down

Sleep between adding aws tags.
Break after tagging.
Merge pull request #857 from edx/feanil/fix_abbey

Break after tagging.
Replace null reference with empty string
Update cache prefix using EDXAPP_ENV_EXTRA_VARS.
Update to have a new flag for updating the staticfiles KEY_PREFIX.
Update cms and preview env configs.
Use the build number instead of the time for the cache key.
Add the triple to make the key more unique.
Update triple order.
Merge pull request #858 from edx/feanil/always_update_cache_prefixes

Feanil/always update cache prefixes
Spell things correctly.
Merge pull request #859 from edx/feanil/always_update_cache_prefixes

Spell things correctly.
Have elastic search start, but not restart each time
edx-west: parameterize machine names in playbooks

Conflicts:
	playbooks/edx-west/prod-app.yml
	playbooks/edx-west/prod-worker.yml
	playbooks/edx-west/stage-app.yml
	playbooks/edx-west/stage-worker.yml
validate machine var, remove migrate_db prompt

Added a validation on the machine variable, expected to be passed in
from the command line now, so that the worker play only works on
machines named "util" and the app play on machines named "app".
Otherwise it would be too easy to mix those up.

Now that we're using -e command line options, it's easier to use this to
specify the "modify_db" variable than prompt_vars.  Having every install
block on this question before was such a hassle!  Now we just won't
migrate unless you explicitly say so on the ansible command with
"migrate_db=yes" or "migrate_only=yes".

Conflicts:
	playbooks/edx-west/carnegie-prod-app.yml
	playbooks/edx-west/carnegie-prod-worker.yml
	playbooks/edx-west/cme-prod-app.yml
	playbooks/edx-west/cme-prod-worker.yml
	playbooks/edx-west/stage-app.yml
Unicorn branch merged, reverting forum version to master
Merge pull request #862 from edx/cg/restore_forum_version

Unicorn branch merged, reverting forum version to master
Merge pull request #855 from edx/cg/add_cas_variables

Added CAS settings to edxapp
Added back restart when the service has been upgraded