Set correctly the messaging driver to use in tests

Depending of the order of the tests executions, the driver can be the
previous configured one. But some tests are written to work on a
specific driver

This change sets the fake driver by default.

It also removes useless mock in test_log_handler.

Change-Id: Ic49bb9aec2e537e55a98315eba8dc97fbb18f96b
Merge "Set correctly the messaging driver to use in tests"