Add a hacking check to block scenario manager in api tests

This commit adds a new hacking check to ensure that the manager class
from the scenario tests, OfficialClientManager, isn't used in the API
tests. There is already a hacking rule preventing imports of the
official clients, T102. But, the official clients could still be used
through the scenario tests which wouldn't be caught by T102. This
attempts to close that gap by adding a new hacking check for
OfficialClientManager.

Change-Id: I608a1319c136118947e3df74fa88f7124011caa4
Fix "create a flavor" tests for strong validation

On Nova v2.1/v3 API,  the input validation of "create a flavor" API
has become more strict. As the result it does not allow " 1024 " as
ram size, and does not allow "" as flavor id.

This patch fixes the related tests for passing these tests.

Change-Id: I58a8cc8fd89a12495ed995e06dbd396a82f6ec71
Closes-Bug: #1336173
Merge "Fix "create a flavor" tests for strong validation"
Merge "Add a hacking check to block scenario manager in api tests"
Merge branch 'master' of https://github.com/openstack/tempest