Factor out the shared code to wait for a log force into a new helper.
This helper uses the XLOG_FORCED_SHUTDOWN check previous only used
by the unmount code over the equivalent iclog ioerror state used by
the other two functions.

There is a slight behavior change in that the force of the unmount
record is now accounted in the log force statistics.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>