Replace try...except block with assertRaises

So the test logic looks tidy and clean.

Change-Id: I8415fbe1d4c0ce59c5c9f173240fcd6eb15b0c63
Remove oslo uuidutils.generate_uuid from heat code

`uuidutils.generate_uuid' is going to be removed from oslo, so we need
to remove the call from heat code.

Change-Id: Iba9f86d8b8ec5ebaf4e80e6b729e372816bd5723
Partial-Bug: #1253497
Merge "Remove oslo uuidutils.generate_uuid from heat code"
Merge "Replace try...except block with assertRaises"