updating gather_assets to use paver instead of rake
don't update rake gem on jenkins
typo fix
Changing  to {{ for EDXAPP_PREVIEW_LMS_BASE
Merge pull request #1378 from edx/han/cherrypick

Han/cherrypick
Make devpi optional for edxapp

To enable, set the `edxapp_devpi_enabled` variable to `true` and set
edxapp_pypi_local_mirror to point to wherever devpi is installed.
Add devpi_host setting to devpi role

Allow specifying a different host than localhost.
Allow restart handler to run when updating conf

Running the edxapp role with -t edxapp_cfg requires the app to be
restarted.
Migrate all enabled service variants databases
Add IONISX_AUTH to edxapp’s auth config
updated edxapp ansible role to include the ability to enable third party authorization
Changed variables to uppercase and added defaults based on feedback.