Functional test UpdateStackTest

This is a port of tempest.api.orchestration.stacks.stack_update
in an effort to reproduce the postgres race described in
bug #1370865.

Subsequent changes will create an experimental postgres check job and
a change to the test which runs test_stack_update_add_remove enough
times to triger the race.

Change-Id: I8aee26e29f242b11a5d3c8d56a859ae770be86c2
Related-Bug: #1370865
Merge "Functional test UpdateStackTest"