MORE Add fsal_filesystem object and supporting commonlib code

Signed-off-by: Frank S. Filz <ffilzlnx@mindspring.com>
MORE VFS

Signed-off-by: Frank S. Filz <ffilzlnx@mindspring.com>
Use fsal_filesystem in FSAL_GPFS to refine multiple filesystem support

With this change, FSAL_GPFS now supports sub-mounted filesystems as part
of an export.

Signed-off-by: Frank S. Filz <ffilzlnx@mindspring.com>