package/mender: create directory containing Mender state script

Mender state-scripts are essentially "hooks" that can be provided to
influence the update flow.

They should be placed inside /etc/mender/scripts and the directory must
contain a file containing the current state-script format version. It is
currently "2".

Signed-off-by: Mirza Krak <mirza.krak@northern.tech>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>