subtests: Fix docker subtests mainly problem with cleanup.

Signed-off-by: Jiří Župka <jzupka@redhat.com>
dockertest: Makes docker exception more pickle-able.

Signed-off-by: Jiří Župka <jzupka@redhat.com>
dockertest: Separate subsubtests more precisely to separate processes.

It allows much simpler subsubtests starting and configuration
moreover it allows simpler simultaneous run of subsubtests without
they influence in framework side. Other words it is only necessary
deal with collision of subsubtests in system env during simultaneous run.

Signed-off-by: Jiří Župka <jzupka@redhat.com>
dockertest: Speed up subsubtest config creating by deep copy-able version.

Creation of subsubtests instance took quite a long time because
deep copy of configuration took a long time.

Signed-off-by: Jiří Župka <jzupka@redhat.com>