Assemble: fix --force assembly of v1.x arrays which are recovering.

Assemble: fix --force assembly of v1.x arrays which are recovering.

1.x metadata allows a device to be a member of the array while it
is still recoverying.  So it is a working member, but is not
completely in-sync.

mdadm/assemble does not understand this distinction and assumes that a
work member is fully in-sync for the purpose of determining if there
are enough in-sync devices for the array to be functional.

So collect the 'recovery_start' value from the metadata and use it in
assemble when determining how useful a given device is.

Reported-by: Mikael Abrahamsson <swmike@swm.pp.se>
Signed-off-by: NeilBrown <neilb@suse.de>