The 5.32.0 release of oslo_messaging included the following change to the
Fake driver:
https://git.openstack.org/cgit/openstack/oslo.messaging/commit/?id=d1dac1c11d357aa8391de7e62f4d003eb820948d
Which means that FakeExchanges are now shared between all
FakeExchangeManager instances. This broke the unit tests in Heat.
This patch effectively reverts the change in oslo_messaging by isolating
FakeExchanges to individual FakeExchangeManger instances once more.
Change-Id: I6c53f477b17247958be7bd6056136bc9f7f50865
Closes-Bug: #1718780