Enable cinder server to be run in SSL mode

This commit allows one to specify ca, cert and key file
to run cinder server in SSL mode

Note: The flag use_ssl per se is not used in cinder yet,
its purpose here it to verify collateral parameters.

Change-Id: Icc373830421f2254692eb8c7baad05a13e6e1e76
(cherry picked from commit 131108aa089fdd66dcd0c46a2acf99c3d21548d7)