Use a signal name->sigval and sigval->signal name mapping
Use a signal name->sigval and sigval->signal name mapping

We can avoid recalculating and creating these by just having these
mappings be module level constants that are created on import time
and avoid recreating them again and again as needed.

Change-Id: Idaf771dc7c7652d35005f0d767bd857c0547b0fe

poznyakandrey/oslo.service,openstack/oslo.service,citrix-openstack-build/oslo.service