dm thin: detect metadata device resizing

Allow the dm thin pool metadata device to be extended.

Whenever a pool is resumed, detect whether the size of the metadata
device has increased, and if so, extend the metadata to use the new
space.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

diff --cc drivers/md/dm-thin-metadata.c
Simple merge

diff --cc drivers/md/dm-thin-metadata.h
Simple merge

diff --cc drivers/md/dm-thin.c
Simple merge