support proposed/* branches

Provide support for named proposed branches for selection logic

This syncs the get_release_name_from_branch() function from grenade.

Change-Id: I1adabf07cdc3ea6863cd30d8b6454fb40fc20288
XenAPI: Add exit point after JEOS installation

If the user only want to run the installation of Ubuntu - to export the
template as an xva, it just needs to specify a non-empty value for:

EXIT_AFTER_JEOS_INSTALLATION

And the script will exit after the jeos template has been created.

Change-Id: I558e2f2b18ee23c15c7e46e2f7e74543cf26b750
XenAPI: Fix vimrc

DevStack installs a default minimal .vimrc file for the stack user.
Unfortunately the `syntax on` config line is not recognised by the vim
installed in DomU. It results in an annoying message being displayed
whenever the user is using vi. To avoid this issue, removing the `syntax
on` line.

Change-Id: I224465cc3cdba3464ea0a9a751f250ecb6ddc9f3
XenAPI: Always update apt sources

If an appliance is used as a base OS, the user might want to use that in
a different region. With this change we always update the used mirrors
in the template.

Change-Id: I7a119664efac1124e54064311c243c63c2a7944b
Merge "support proposed/* branches"
Merge commit 'refs/changes/03/127603/2' of git://gold.eng.hq.xensource.com/git/github/openstack-dev/devstack into tmpbranch
Merge commit 'refs/changes/16/128716/1' of git://gold.eng.hq.xensource.com/git/github/openstack-dev/devstack into tmpbranch
Merge commit 'refs/changes/17/128717/1' of git://gold.eng.hq.xensource.com/git/github/openstack-dev/devstack into tmpbranch
Merge commit 'refs/changes/18/128718/1' of git://gold.eng.hq.xensource.com/git/github/openstack-dev/devstack into tmpbranch