Fix UnboundLocalError error

This change corrects the UnboundLocalError exception that
can occur if something bad happens on reconnect to RabbitMQ

Closes-Bug: #1272271

Change-Id: I9e157810caa7a45e9a61ec571cfe9024fabacf93
Use stevedore's make_test_instance

Replace the use of TestManager with make_test_instance
to get an instance of the type of manager expected.
The old TestManager class is deprecated

Change-Id: I717c0296bf8ae07b1dad8f0045bfe12c8620ad0a
Partial-bug: #1273455
Merge "Use stevedore's make_test_instance"
Merge "Fix UnboundLocalError error"