gfs2: Clear flags when withdraw prevents xmote

There are a couple places in function do_xmote where normal processing
is circumvented due to withdraws in progress. However, since we bypass
most of do_xmote() we bypass telling dlm to lock the dlm lock, which
means dlm will never respond with a completion callback. Since the
completion callback ordinarily clears GLF_LOCK, this patch changes
function do_xmote to handle those situations more gracefully so the
file system may be unmounted after withdraw.

A very similar situation happens with the GLF_DEMOTE_IN_PROGRESS flag,
which is cleared by function finish_xmote(). Since the withdraw causes
us to skip the majority of do_xmote, it therefore also skips the call
to finish_xmote() so the DEMOTE_IN_PROGRESS flag needs to be cleared
manually.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>