heat_keystoneclient ensure admin client respects SSL options

The SSL related fixes merged under blueprint clients-ssl-options
and bug #1213122 missed the transient client created by
create_trust_context, so add the required options to
service_admin_creds, such that any client created using the
service admin credentials will use SSL if configured to do so.

Change-Id: Iab25c5ee6ec5cba9aaaccb93ce4e680e2f9cd9ac
Related-Bug: #1213122
Merge "heat_keystoneclient ensure admin client respects SSL options"