Show message when job is waiting in queue or for locks

Jobs submitted via the standard command line utilities didn't give any
indication that anything is happening while they were waiting in the job
queue (e.g. due to other jobs using all worker threads) or acquiring
locks. This could be very confusing for people not familiar with Ganeti's
architecture. Now they'll show a message after the first WaitForJobChanges
timeout.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>