The flags ``--db-nb-pid`` and ``--db-sb-pid`` are corected to be
``--db-nb-pidfile`` and ``--db-sb-pidfile`` respectively. See here for
reference:
6c6a7ad1c6/utilities/ovn-ctl (L1045)
Closes-Bug: #2018436
Change-Id: Ic1e8768374566eb2198302807ecc644a19cd3062