Add scratch directory for NFS upcall state storage
When the /var/lib/nfs/v4recovery directory is not present, NFSD cannot
record the upcall state and cannot end the 90-second grace period on
startup. This is true even when NFS4 is not being served according to
nfsstat.
More details and discussion here:
https://lkml.org/lkml/2012/6/11/206
