Update jenkins playbook to reflect changes to role.
Use a branch until aws fix is in master.
Be able to create stacks from a list of parameters.
Remove the remove_file function call since the function doesn't exist yet.
Add the ability to install extra system packages.
Add the ability to set parent dns zone.
Add environment var and gh_users.

Replace 'dev' with a variable so that we can start using the playbook with other environments.

Use the gh_users role instead of creating users in the common role.
Allow instances to reach gpg keyservers.
Conditionally update cloudfromation stacks.
Don't try to start edxapp running as a worker.
Remove explicitly setting the edx_platform_commit.
Merge pull request #453 from edx/feanil/pre_stage

Feanil/pre stage