Revert the version of Horizon used for tests to stable/grizzly

Change-Id: I8068b8bf095d1314a667d22dfa7623a3a19c8c4e
Signed-off-by: Rosario Di Somma <rosario.disomma@dreamhost.com>
Merge pull request #26 from rodis/stable/grizzly

Revert the version of Horizon used for tests to stable/grizzly