Add volume plugin method and modify plugin file to adapt to docker v1.12

Change-Id: I3cc80b814818eda93c214476eedbcc54fa3694ea
Closes-Bug: #1607990

etc/fuxi.spec

@@ -0,0 +1 @@
+http://127.0.0.1:7879

fuxi/controllers.py

@@ -225,3 +225,8 @@ def volumedriver_list():
     app.logger.info(_LI("Get volumes from volume providers. "
                         "Volumes: {0}").format(docker_volumes))
     return flask.jsonify(Err=u'', Volumes=docker_volumes)
+
+
+@app.route('/VolumeDriver.Capabilities', methods=['POST'])
+def volumedriver_capabilities():
+    return flask.jsonify(Capabilities={'Scope': 'global'})

setup.cfg

@@ -37,7 +37,7 @@ data_files =
     /etc/fuxi/rootwrap.d =
         etc/rootwrap.d/fuxi.filters
     /usr/lib/docker/plugins/fuxi =
-    	etc/fuxi.json
+        etc/fuxi.spec
 
 [build_sphinx]
 source-dir = doc/source