Remove ConfFixture from toplevel public API

There's no need to make the fixtures, testtools, etc. libraries a
runtime requirement, so let's move it from the toplevel oslo.messaging
API so you need to explicitly import it.

Change-Id: I9e2f32a898d78489f2d8d9c218c81f35cda14e34

doc/source/conffixture.rst

@@ -0,0 +1,9 @@
+----------------------
+Testing Configurations
+----------------------
+
+.. currentmodule:: oslo.messaging.conffixture
+
+.. autoclass:: ConfFixture
+   :members:
+

oslo/messaging/__init__.py

@@ -13,7 +13,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from .conffixture import *
 from .exceptions import *
 from .localcontext import *
 from .notify import *

requirements.txt

@@ -1,9 +1,6 @@
 oslo.config
 stevedore
 
-# for oslo.messging.conffixture
-fixtures>=0.3.12
-
 # for timeutils
 iso8601
 

test-requirements.txt

@@ -5,6 +5,7 @@ flake8==2.0
 hacking>=0.5.6,<0.7
 
 discover
+fixtures>=0.3.12
 mox>=0.5.3
 python-subunit
 testrepository>=0.0.13