Allow tests to run outside tox

When using a test runner outside of tox (for example
using py.test directly against test files, one of several
ways to enable faster and more specific testing)
oslo.messaging.conffixture is not imported and text/base fails
to compile.

This change gets things working and otherwise has no impact.

Change-Id: Ibac6ae0a73aa55522b248a26b9a4b82455f8fce6
Merge "Allow tests to run outside tox"