Database not needed for RPC serializer tests
Database not needed for RPC serializer tests

The following test classes don't access the database, so make them
extend NoDBTestCase.

 - TestJsonPayloadSerializer
 - TestRequestContextSerializer

$ tox -e py27 nova.tests.unit.test_rpc

Runtime before: 27.3501 sec
Runtime after: 4.7279 sec

Change-Id: Id06d92e28a9aecbb8e4975e95a8f11b0b2e79ae2

alaski/nova,Juniper/nova,klmitch/nova,klmitch/nova,zhimin711/nova,mahak/nova,bigswitch/nova,vmturbo/nova,openstack/nova,vmturbo/nova,openstack/nova,mikalstill/nova,jianghuaw/nova,BeyondTheClouds/nova,bigswitch/nova,cernops/nova,cloudbase/nova,phenoxim/nova,rahulunair/nova,Juniper/nova,CEG-FYP-OpenStack/scheduler,dims/nova,rajalokan/nova,openstack/nova,Juniper/nova,rajalokan/nova,alaski/nova,mahak/nova,cyx1231st/nova,klmitch/nova,NeCTAR-RC/nova,vmturbo/nova,mikalstill/nova,vmturbo/nova,cyx1231st/nova,cloudbase/nova,BeyondTheClouds/nova,gooddata/openstack-nova,hanlind/nova,rahulunair/nova,gooddata/openstack-nova,dims/nova,mahak/nova,cloudbase/nova,sebrandon1/nova,jianghuaw/nova,Juniper/nova,rajalokan/nova,gooddata/openstack-nova,rajalokan/nova,jianghuaw/nova,sebrandon1/nova,jianghuaw/nova,hanlind/nova,zhimin711/nova,klmitch/nova,cernops/nova,gooddata/openstack-nova,cernops/nova,CEG-FYP-OpenStack/scheduler,hanlind/nova,BeyondTheClouds/nova,NeCTAR-RC/nova,phenoxim/nova,rahulunair/nova,sebrandon1/nova,mikalstill/nova