Add module for waiting until action is finished

[stdevel]

For some actions (e.g. installing patches) it is required to wait until they are finished before the next step (e.g. rebooting the host) is executed. For this specific example, we can't rely on the Uyuni task scheduler, as requests are in mixed order sometimes. A module like stdevel.uyuni.wait_for_task could be a benefit. Another option would be to add wait parameters to the corresponding modules.

Requires #37.