Docker: Version 0.1.1 updates

*  Support custom and/or private test modules and/or configurations.
   Otherwise modifying the default configs. will make version control
   grumpy.  Anything (includeing replacement defaults) defined inside
   the new config_custom directory tree will override content from the
   config_defaults (formerly config.d) tree.

*  Subtests now support optionally setting the # of test iterations from
   their config section with the 'iterations' key.  If not present,
   it defaults to the class-attribute value.

*  Added additional comments in various places, further clarifing
   decisions.

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