Drop msgpack dependency

We've been using msgpack just to pack the API document into sqlite
binary documents. This is easily achievable with json. We can pull
msgpack in again when there's a real use case for it.

Change-Id: I60e31806edafd71de62a1809f047a8ad772094cc

marconi/queues/storage/sqlite/driver.py

@@ -14,10 +14,10 @@
 # limitations under the License.
 
 import contextlib
+import json
 import sqlite3
 import uuid
 
-import msgpack
 from oslo.config import cfg
 
 from marconi.common import decorators
@@ -126,10 +126,10 @@ class DataDriver(storage.DataDriverBase):
         :param o: a Python str, unicode, int, long, float, bool, None
                   or a dict or list of %o
         """
-        return sqlite3.Binary(msgpack.dumps(o))
+        return sqlite3.Binary(json.dumps(o))
 
     sqlite3.register_converter('DOCUMENT', lambda s:
-                               msgpack.loads(s, encoding='utf-8'))
+                               json.loads(s, encoding='utf-8'))
 
     @staticmethod
     def uuid(o):

marconi/queues/storage/sqlite/queues.py

@@ -77,10 +77,9 @@ class QueueController(base.QueueBase):
         if project is None:
             project = ''
 
-        # msgpack of {} is "\x80"
         self.driver.run('''
             insert or ignore into Queues
-            values (null, ?, ?, "\x80")
+            values (null, ?, ?, "{}")
         ''', project, name)
 
         return self.driver.affected