Update .coveragerc after the removal of openstack directory

The openstack directory was used to keep codes from oslo-incubator,
we have retired oslo-incubator,so don't use this directory any more.

Change-Id: I9ad0065bcc564dd21457ce58fc32372b22ad29cb

Author: DeepakJonAI

.coveragerc

@@ -1,7 +1,7 @@
 [run]
 branch = True
 source = octavia
-omit = octavia/tests/*,octavia/openstack/*
+omit = octavia/tests/*
 
 [report]
 ignore_errors = True