quantum-plugin-nicira imports mock but was not used

The import of mock prevents quantum from starting when using the
nvp plugin since mock is not an install dependency. This patch
removes where mock was imported but did not actually need to be.

Fixes bug 1097451

Change-Id: If1569d437fe523e4fac8d686da52b0508ca1cbf3

quantum/plugins/nicira/nicira_nvp_plugin/api_client/common.py

@@ -17,16 +17,13 @@
 #
 
 import httplib
-import mock
 
 
 def _conn_str(conn):
     if isinstance(conn, httplib.HTTPSConnection):
         proto = "https://"
     elif isinstance(conn, httplib.HTTPConnection):
         proto = "http://"
-    elif isinstance(conn, mock.Mock):
-        proto = "http://"
     else:
         raise TypeError('_conn_str() invalid connection type: %s' % type(conn))