subtests..build: Download busybox from internet

Download busybox (GPLv2) from the public repository in setup() phase instead
of package dependency.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
Docker: Add dockertest.docker_daemon module

*  Since python-docker-py is just an example reference implementation
   we should not rely on it for testing.  However, several tests
   need to obtain information directly from the daemon.  The
   docker_daemon module simplifies this while allowing for future
   expansion.

*  Update version test to use dockertest.docker_daemon instead of
   custom HTTP request when python-docker-py is not available.

*  Updated documentation.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
Signed-off-by: Chris Evich <cevich@redhat.com>
Docker: fix subtest C++-like names to python ones

Rename following methods to pythonic convention:
subtest.parentSubtest => subtest.parent_subtest
subtest.subStuff => subtest.sub_stuff

and increase the API minor number.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
dockertest.subtest: Add missing log variable

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
subtests..run_simple: Refactor this test as SubSubtests

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
subtests..run_simple: Minor cleanups

*  Removed redundant ``config_section`` attributes
   from subsubtests (they're automatically discovered)

*  Folded ultra-simple true/false modules into the main
   module (left ``run_signal`` separate).

*  Accidentally reordered Lukáš commits, needed to
   fixup subStuff -> sub_stuff and parentSubtest -> parent_subtest
   due to 0.4.1 interface change (expected).

*  Fixed subtests..psa to remove stop file as per
   Lukáš Doktor <ldoktor@redhat.com>

*  Increased run_simple:run_signal post-signal timeout in case
   downloading the image is needed.

*  Updated documentation

Signed-off-by: Chris Evich <cevich@redhat.com>
dockertest.images: Fixup pylint finding

Timeout parameter was defaulted in ancestor class but
I forgot to update in child class also.

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