Warn the user about too small array size

Warn the user about too small array size

If single-disk RAID0 or RAID1 array is created, user may preserve data on
disk. If array given size covers all partitions on disk, all data will be
available on created array. If array size is too small (not covers
all partitions), data will be not accessible.
This patch introduces warning message during array creation if given size
is too small. User may interrupt creation process to avoid data loss.

Signed-off-by: Krzysztof Wojcik <krzysztof.wojcik@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>