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
HEAT_FETCHED_TEST_IMAGE may not be defined in some cases.

Some scripts that source stackrc use set -u, which will error
when unknown variables are accessed

Change-Id: I5af2d58475e1793dfa728b7ce9180fcbba1145e9