XenAPI:  Increase DomU's memory

Devstack has been increasing in complexity, and if we use too
much of our memory it can lead to fragmentation which in turn
causes a DomU error and a failure of random tests.

Change-Id: Ide9cc84625caed4e35a64a47ee1e92a6cd567651
XenAPI: Update DomU to Ubuntu Saucy

Driven by a race condition in LVM being hit in the tempest
tests.  This is a locking race between a file lock and a
semaphore which is fixed in 2.02.96-5.

Change-Id: I8a8c215c90a0602288292ffd06b7694d2db6219e