Make container support optional.

At the moment, both `ansible-container==0.3` and `docker-compose`
depend on an old version of the `requests` package which conflicts
with what the OpenStack libraries (needed for the "vm" functionality)
require.  Until we can switch to `ansible-container==0.9`, make
container support optional so people can install and run `tm_deploy
vm` without worrying about fixing Python dependencies.

Fix #68

setup.py

@@ -109,7 +109,6 @@ def get_version():
        'apache-libcloud>=1.3.0',
        'boto>=2.48',
        'boto3>=1.4.1',
-       'docker-py>=1.10.6',
        'PyYAML>=3.11',
        'psycopg2>=2.6.1',
        'shade>=1.12.1',
@@ -119,10 +118,10 @@ def get_version():
         # We still depend on ansible-container 0.3. They have made a major jump
         # to version 0.9 and we are still refactoring our repository.
         # For now, we make container deployment optional, because it causes
-        # multiple problems with package dependencies.
+        # multiple problems with package dependencies.  See e.g. #68
        'container': [
-           'ansible-container>=0.3.0,<=0.4'
+            'ansible-container>=0.3.0,<=0.4',
+            'docker-py>=1.10.6',
         ],
     },
 )
-