Remove a bunch of uuid.uuid4() calls from tests, and use static UUIDs
instead.
We generally use static UUIDs to make test runs reproducible and to make
it easier to track odd failures that repeat in the gate.
Readability of tests is also improved by using meaningful names like
VOLUME_ID or SNAPSHOT_ID rather than just uuid4().
So, do more of that.
Some care has to be taken in test classes that create lots of volumes,
such as BackupBaseDriverTestCase, because random UUIDs were previously
allowing volumes used by different tests to not collide with each other.
More static IDs have been added to account for this.
Change-Id: I372d27367b730f4606bc0ea84a9b322d45d1cbbe
b83c446e52