Allow for sqla 0.8... finally

It turns out we actually support sqla 0.8.x... yay!

Set this in global requirements so we start running 0.8.4 in the
gate. Which might also have interesting performance benefits.

This requires an update of the requirements integration tests
(which are in the pbr tree.... o_O)

Depends-On: I01b2b7c78e7e7144280c98cdbbe29b012a8a8d93

Change-Id: I7a22dbb47e85f3adf5d43583f5b9bac4f65fde14
Add XenAPI to OpenStack dependencies

This way, the XenAPI package will be mirrored by the OpenStack pypi
mirror, so it could be installed in the gate.

Change-Id: I185f9ccf26c59a339f94f6918d695f28a5eb5b62