mdadm: add util-linux-blockdev ptest dependency

07revert-inplace test logs contain the following:
func.sh: line 335: /sbin/blockdev: No such file or directory

Add the missing util-linux-blockdev dependency.

Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
(cherry picked from commit a15cd04f)
Signed-off-by: Steve Sakoman <steve@sakoman.com>