ctdb-scripts: Use CTDB_NFS_SHARED_STATE_DIR in nfs-ganesha-callout

ctdb-scripts: Use CTDB_NFS_SHARED_STATE_DIR in nfs-ganesha-callout

Rename CTDB_NFS_STATE_MNT to CTDB_NFS_SHARED_STATE_DIR.  It doesn't
have to be a mount but can be any directory in a cluster filesystem.
There are plans to also use CTDB_NFS_SHARED_STATE_DIR for
statd-callout, so the name might as well be better.

CTDB_NFS_SHARED_STATE_DIR is now mandatory when GPFS is used.  This is
much saner that choosing the first GPFS filesystem - if the state
directory changes then connection metadata can be lost.

Drop CTDB_NFS_STATE_FS_TYPE.  The filesystem type is now determined
from CTDB_NFS_SHARED_STATE_DIR and it is now checked against supported
filesystems.  This will catch the case when the filesystem for the
specified directory has not been mounted and the filesystem for the
mountpoint (e.g. ext4) is not a supported filesystem for shared state.

A side-effect is that the filesystem containing
CTDB_NFS_SHARED_STATE_DIR must be mounted when nfs-ganesha-callout is
first run.

Signed-off-by: Martin Schwenke <mschwenke@ddn.com>