checks before deleting kwargs from the context
checks before deleting kwargs from the context

Make sure to check if the kwarg is there before deleting it.

bug 1074422

Change-Id: I66f5338b100f3c16f7e0ca0382ecfea22b099726

citrix-openstack/build-trove,hplustree/trove,mmasaki/trove,citrix-openstack-build/trove,zhujzhuo/openstack-trove,redhat-openstack/trove,citrix-openstack/build-trove,cp16net/trove,fabian4/trove,hplustree/trove,mmasaki/trove,fabian4/trove,fabian4/trove,citrix-openstack-build/trove,citrix-openstack-build/trove,zhujzhuo/openstack-trove,denismakogon/trove-guestagent,cp16net/trove,denismakogon/trove-guestagent,zhangg/trove,mmasaki/trove,zhujzhuo/openstack-trove,changsimon/trove,citrix-openstack/build-trove,redhat-openstack/trove,openstack/trove,cp16net/trove,changsimon/trove,redhat-openstack/trove,openstack/trove,zhangg/trove,changsimon/trove