Fix race between --create and --incremental

This modifies locking in Create to eliminate a situation where
--incremental can assemble a device between write_init_super() and
add_disk(), which causes Create to fail.

It sporadically occurs e.g. when metadata is written on a device,
causing an udev change event which triggers mdadm --incremental.

Signed-off-by: Artur Paszkiewicz <artur.paszkiewicz@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Create: don't default to bitmap=internal when it is not supported

For large arrays (component size > 100GB) if write-intent bitmap is not
enabled, then it is set by default to "internal", even if the metadata
format does support internal bitmaps, which causes Create to fail.

This patch adds checking if add_internal_bitmap is set in the
superswitch before setting bitmap_file to "internal".

Signed-off-by: Artur Paszkiewicz <artur.paszkiewicz@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>