Fix docstring typo in jqueue._JobProcessor._MarkWaitlock

epydoc complained:
“File …/ganeti/jqueue.py, line 886, in
ganeti.jqueue._JobProcessor._MarkWaitlock
  Warning: Redefinition of type for job”

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