statd: Decouple statd's state directory from the NFS state directory

To allow greater flexibility to where statd's state is kept,
statd's state path can now be decoupled from the normal
NFS state directory.

In configure.ac, the NSM_DEFAULT_STATEDIR definition will now define
the path to where the state information is kept.  The default
value, /var/lib/nfs, can be redefined with the --with-statdpath
flag.

Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>