nfs-utils: create /var/lock/subsys

The NFS server needs to create files in /var/lock/subsys/, but this
directory doesn't exist in our skeleton. This commit makes sure it
gets created by the S60nfs startup script, which fixes the operation
of the NFS server (tested with rpcbind).

Reported-by: Ofer Heifetz <oferh@marvell.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>