subtests...run_volumes: Fix bugs, improve logging.

*  It was difficult to see what went wrong when running
   these tests.  Added some helpful messages.

*  Switched config from using old string.template to
   new string format /w dictionary subs.

*  Fixed problem with not checking test paths exist on
   host, and are directory.

Signed-off-by: Chris Evich <cevich@redhat.com>