Expand README file with information for new users

This change expands README.md and adds docs/mkcloud.md with the following
sections:

* Installation, steps needed to prepare the host in order to use the
  automation scripts
* Configutation, brief description of the most important configuration
  keys and pointing out the complete list is available using `mkcloud -h`.
* Usage, example usage to create a cloud and run tempest.
* Contributing, a short description how to contribute to this repository.

This change expands the README file to include a section about the
'installation' of the automation scripts and steps needed to prepare
the host in order to use the automation scripts.
qa_crowbar: Move SLES repos handling to function

Preparation for adding local repository support.
qa_crowbarsetup: Add possibility to ignore mounts

For some cases it's needed to just bind or nfs mount. This is useful for
the upcoming deps image support.
qa_crowbar: Add local repos support for SLES repos

Use the extracted deps image as source for Cloud dependencies.