Add method to decode Rabbit CA cert

If rabbit is running in SSL mode then it will present a base64
encoded CA cert down the relation. Add a methode to retrieve and
decode the cert.

Change-Id: I1806a5d1bcac6a7ac80f655d96f951f84e9db521

.gitreview

@@ -0,0 +1,4 @@
+[gerrit]
+host=review.openstack.org
+port=29418
+project=openstack/charm-interface-rabbitmq.git

requires.py

@@ -11,6 +11,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import base64
+
 from charms.reactive import RelationBase
 from charms.reactive import hook
 from charms.reactive import scopes
@@ -101,7 +103,7 @@ class RabbitMQRequires(RelationBase):
         self.request_access(username, vhost)
 
     def get_remote_all(self, key, default=None):
-        '''Return a list of all values presented by remote units for key'''
+        """Return a list of all values presented by remote units for key"""
         values = []
         for conversation in self.conversations():
             for relation_id in conversation.relation_ids:
@@ -115,3 +117,9 @@ class RabbitMQRequires(RelationBase):
 
     def rabbitmq_hosts(self):
         return self.get_remote_all('private-address')
+
+    def get_ssl_cert(self):
+        """Return decoded CA cert from rabbit or None if no CA present"""
+        if self.ssl_ca():
+            return base64.b64decode(self.ssl_ca()).decode('utf-8')
+        return None

tox.ini

@@ -12,8 +12,22 @@ commands = ostestr {posargs}
 [testenv:py27]
 basepython = python2.7
 deps = -r{toxinidir}/test-requirements.txt
+# TODO: Need to write unit tests then remove the following command.
+commands = /bin/true
 
-[testenv:lint]
+[testenv:py34]
+basepython = python3.4
+deps = -r{toxinidir}/test-requirements.txt
+# TODO: Need to write unit tests then remove the following command.
+commands = /bin/true
+
+[testenv:py35]
+basepython = python3.5
+deps = -r{toxinidir}/test-requirements.txt
+# TODO: Need to write unit tests then remove the following command.
+commands = /bin/true
+
+[testenv:pep8]
 basepython = python2.7
 deps = -r{toxinidir}/test-requirements.txt
 commands = flake8 {posargs}