remove swiftclient/openstack/common/* in the .coveragerc

There is no swiftclient/openstack/common/* in python-swiftclient.
Therefore, I remove "omit=swiftclient/openstack/common/*"
in the .coveragerc.

Change-Id: Ibf4e4e499cb5538fcd8b1680285294c8a09ad401

Author: zheng yin

.coveragerc

@@ -1,7 +1,6 @@
 [run]
 branch = True
 source = swiftclient
-omit = swiftclient/openstack/common/*
 
 [report]
 ignore_errors = True