Configure heat keystone client for SSL when keystone uses SSL

When SSL is enabled in Keystone, the path to the Keystone CA file
needs to be set in ca_file in the clients_keystone section.

Change-Id: Ic324e09b42a96d0ba31e13f8e8042cb3ac24d0b6
Closes-Bug: 1324207
Merge "Configure heat keystone client for SSL when keystone uses SSL"