When Glance is configured to run with SSL this patch will check
that the certificate and key exist, are readable, and match each
other at boot time. If any of the above conditions fail an friendly
error message is logged directing the operator at a solution.
Previously the keys were not checked until a client connected.
fixes bug: 1160529
Change-Id: I16975608f9ae40ac5b84b3caa52ed5f8e22f296e