engine: explicitly set locale for unit test.

- When running the unit tests on a machine set with
  a locale to fr_FR it would cause the unit test to
  fail as the alternate locale was loaded by default
  instead of en_US. This patch sets the VM locale to
  en_US before the test run.

Change-Id: I7b3d766413ba095e4543ad3f8c3e6d4af7591cf9
Signed-off-by: Alexander Wels <awels@redhat.com>