fix write mostly for add and re-add

The following patch makes it possible to tag a device as write-mostly on
--add and --re-add with a non-persistent superblock array. Previously,
this was not working.

Signed-Off-By: Paul Clements <paul.clements@steeleye.com>
Signed-off-by: Neil Brown <neilb@suse.de>

Manage.c

@@ -341,6 +341,8 @@ int Manage_subdevs(char *devname, int fd,
 						break;
 					}
 			}
+			if (dv->writemostly)
+				disc.state |= (1 << MD_DISK_WRITEMOSTLY);
 			if (ioctl(fd,ADD_NEW_DISK, &disc)) {
 				fprintf(stderr, Name ": add new device failed for %s as %d: %s\n",
 					dv->devname, j, strerror(errno));