Merge pull request #566 from edx/will/devstack-base-box

Set devstack base box to empanada release (RC)
Merge remote-tracking branch 'origin/master' into rc/empanada
Merge remote-tracking branch 'origin' into rc/empanada
Merge pull request #561 from edx/rc/empanada

Rc/empanada
Merge pull request #729 from edx/jarv/focaccia

Jarv/focaccia
Merge branch 'master' into release
Merge pull request #775 from edx/feanil/release-gugelhupf

Feanil/release gugelhupf
Added option to specify migration user and changed to admin user and password vars
devstack vagrantfile: mount "themes" from host

This mounts the "themes" directory on the host.  This will enable people
who have configured "stanford-style" themes to check out their themes on
the host and have it useable in the devstack.

Two things are a bit odd about this that are worth highlighting.

1. For people not using Stanford-style theming, which are most
   developers and certainly everyone at edX.org, this is a wasted
   export.  It doesn't do any harm, but would it be confusing?  I
   think that's OK.

2. The provision steps checks out the other repos that you need
   (edx-platform, cs_comment_service, etc.).  We're not checking out
   the theme repo ourselves here, counting on the user to do so
   yourself later.  I know this isn't consistent, but I couldn't
   plumb through the theming stuff into the rest of devstack
   provision, at least not right now.
Add options for installing and configuring a CAS attribute mapper
Fix devstack and CI breakage.
Pin devstack to the release branch of configuration.
ensure python-mysqldb is installed before we attempt to create_dbs
Add missing variable MKTG_URLS in configuration
Merge pull request #900 from ionis-education-group/mktg-urls-missing

Add missing variable MKTG_URLS in configuration
Correct pre-supervisor location.
Merge pull request #899 from edx/derf/install-mysqldb-before-create_dbs

ensure python-mysqldb is installed before we attempt to create_dbs
Merge pull request #895 from edx/feanil/fix_ci

Fix devstack and CI breakage.
Adding MIGRATE user
Merge pull request #864 from edx/cg/add_migration_user

Added option to specify migration user and changed to admin user and password vars