dockertest.dexpect: Log the executed command

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
dockertest.containers: Add useful tools to DockerContainer(s)

This ugly patch makes it possible to very easily create container
defined by configuration and than interact with it easily. This patch
is not intended for inclusion, it just shows the possibilities and
eventually needs to be redesigned to not look as ugly as is now.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
subtests.docker_cli.interaction: Add new test

This test demonstrates the usage of DockerContainers extended
tools.
1) create container - 1 line
2) attach session - 1 line (6 lines including branch to attach main process
                            or create new attach process)
3) various check, command execution...
4) safe removal of all managed containers

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>