subtests.docker_cli.start: Modify start test to new docker behavior

The `docker start` command should only return 0, when the container
is already running.

https://bugzilla.redhat.com/show_bug.cgi?id=1090071

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
subtests.docker_cli.start: Code and style cleanups

This patch removes duplicite postprocess, adds timeout for bg process
and fixes some pep8 style fixes. There is no real test-logic change.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
Merge branch 'start_simple' of https://github.com/ldoktor/autotest-docker
subtests...start: Fix catchall in cleanup()

Specific exceptions defined for expected/likely error
behavior, anything else is a possible bug somewhere.

Signed-off-by: Chris Evich <cevich@redhat.com>
subtests...start: Simplify configuration

*  Removed unused ``docker_start_force`` option.
*  All tests expected to PASS now, removed option.
*  Made ``check_if_cmd_finished`` into class variable
   for one sub-subtest that uses it.
*  Utilize parent defaults for ``docker_attach``
   and ``docker_interactive`` options.
*  Updated documentation

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