Docker: Segment subtest Init, add enable option

*  Broke down SubTest __init__ into individual
   private methods for each behavior segment
   to make it easier to read/debug.

*  Added ``enable`` configuration (on by
   option ("True" by default) to default
   config section.  Allows individual
   tests to be marked for skipping
   with or without using ``--args``
   csv list.

*  Updated docs.

*  Bumped revision version to 0.5.3 (no interface
   changes)

Signed-off-by: Chris Evich <cevich@redhat.com>
subtests..cp: added cp test

Signed-off-by: James Molet <jmolet@redhat.com>
Merge pull request #43 from cevich/docker_cp

subtests..cp: added cp test
Merge pull request #31 from cevich/debug

Add enable conf. option
fix dockerimport test fail by KeyError if docker-py

(github issue #30)

Signed-off-by: Chris Evich <cevich@redhat.com>
Merge pull request #44 from cevich/import_fix

fix dockerimport test fail by KeyError if docker-py