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 a task to install paver requirements.
Merge pull request #1001 from edx/jarv/add-paver-to-release-branch

Add a task to install paver requirements.
removing npm
fixing pypi mirror
Merge pull request #1003 from edx/han/fix-travis

removing npm
Merge pull request #1004 from edx/jarv/add-paver-to-release-branch

fixing pypi mirror
Setting ssh to allow passwords for devstack
taking out deploy tag to make sure sshd_config is picked up
Simple hipchat integration for logging.
refactoring
Exception handling refactor.
Send exception to Hipchat.
Merge pull request #1011 from edx/han/devstack

Han/devstack
Add a utility play to update the ora2 version installed for edxapp
Merge pull request #1017 from edx/will/ora2-utility-play

Add a utility play to update the ora2 version installed for edxapp
adding certificates to the public images

removing sync'd folder for /vagrant

change identity file default to none

removing check for git identity

typo

typo

adding python-yaml for dumping vars

certs settings changes for local disk generation

adding var dump var

adding template for certs

adding certs to default sites

adding 400 condition to the certs nginx template

updating update script for certs, removing discern

adding cert to help

giving www-data write permission to the web root

typo

adding download url

fixing web root

adding certs download url

adding more config for cert template dir, verify url

moving extra vars into the vagrantfile

adding verify url to vagrantfile

syntax

look for valid.html

adding ownertrust export

adding the trust import

removing skip-tags for reconfigure

upgrading to latest released ansible

adding carriage return to owner trust

setting cert urls in extra vars

moving extra vars to vagrantfile

adding new accept_hostkey parameter to all git calls

set key_file

changing dir for userknownhostsfile

adding more verbosity

changing knownhostsfile in environment

don't use userknownhostsfile

setting accept_hostkey back to yes

adding .ssh dirs for the 1.5 git module

adding certs nginx site
Merge pull request #1014 from edx/e0d/hipchat

E0d/hipchat
Merge pull request #1019 from edx/jarv/ansible-1.5-and-certs

Jarv/ansible 1.5 and certs
disabling /vagrant sync'd folder