Hbal.hs: move job execution functions to Jobs.hs

Ganeti.Jobs now holds functions that can be used to submit and monitor the
status of jobs. In particular, execJobsWait and waitForJobs are factored
out of Hbal.hs.

Signed-off-by: Dato Simó <dato@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>