Allow heat tests to use already uploaded test image

If $HEAT_FETCHED_TEST_IMAGE is set then tempest is configured to
use the image named $HEAT_FETCHED_TEST_IMAGE for any orchestration
tests which require an image.

Fallback to checking $HEAT_CREATE_TEST_IMAGE and invoking
diskimage-builder if necessary.

The intent is to use Fedora 20 as the test image for gating
since this image has heat-cfntools already installed.

Change-Id: I177ae091a641ba99fd4c618e30a39c5148ae617f
Merge "Allow heat tests to use already uploaded test image"
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
Fix xenapi functions' tests

The tests got outdated, this fix makes the tests pass again.

Change-Id: Iadddfbf34bf79ba455811645e766c2f3d0fcca84
Workaround missing zip snapshot

At the moment, xenserver installation depends on github snapshots.
Unfortunately, git.openstack.org does not have that capability. This
fix includes:

 - Exit with error code, if a download fails
 - create proper urls, even if they are using the git protocol
 - set git base to github - so we are able to do snapshots

Fixes bug: 1259905

Change-Id: I8d0cf8bf8abb16ee0a4b138a6719409c75e7a146