qa_crowbarsetup: chef exit codes and check if zypper is running

This patch adds the following helper functions:

* `wait_if_running` checks if there is a process running and waits until the
process exits, this is useful if you want to use zypper and want to check
that there is no other zypper process running in the server.
* `die` prints a message to stderr and exit with the error code passed as argument.