tests: add workaround for older mdadm

Some older instancies of 'mdadm' opened legs in RW and
closed and opened again and expected exlusive access.
But here udev rule can be fired - so on these versions
slow down whole mdadm runtime by using strace, to
give system a bit more time to finish udev rule.

test/shell/lvm-on-md.sh

@@ -27,6 +27,18 @@ _clear_online_files() {
 
 . lib/inittest
 
+which mdadm || skip
+
+STRACE=
+[ "$DM_DEV_DIR" = "/dev" ] && mdadm -V 2>&1 | grep " v3.2" && {
+	# use this 'trick' to slow down mdadm which otherwise
+	# is racing with udev rule since mdadm internally
+	# opens and closes raid leg devices in RW mode and then
+	# tries to get exlusive access to the leg device during
+	# insertion to kernel and fails during assembly
+        # There could be more affted version of mdadm.
+	STRACE="strace -f -o /dev/null"
+}
 
 # This stops lvm from taking advantage of hints which
 # will have already excluded md components.
@@ -109,7 +121,7 @@ test ! -f "$RUNDIR/lvm/vgs_online/$vg"
 # should not show an active lv
 not dmsetup info $vg-$lv1
 
-mdadm --assemble "$mddev" "$dev1" "$dev2"
+$STRACE mdadm --assemble "$mddev" "$dev1" "$dev2"
 aux udev_wait
 
 not pvs "$dev1"
@@ -264,7 +276,7 @@ test ! -f "$RUNDIR/lvm/vgs_online/$vg"
 not dmsetup info $vg-$lv1
 
 # start the md dev
-mdadm --assemble "$mddev" "$dev1" "$dev2"
+$STRACE mdadm --assemble "$mddev" "$dev1" "$dev2"
 aux udev_wait
 
 not pvs "$dev1"