virfile: added GPFS as shared fs
    
    Added GPFS as shared file system recognized during live migration
    security checks.
    
    GPFS is 'IBM General Parallel File System' also called
    'IBM Spectrum Scale'
    
    BUG: https://bugzilla.redhat.com/show_bug.cgi?id=1679528
    
    Signed-off-by: Diego Michelotto <diego.michelotto@cnaf.infn.it>
    Signed-off-by: Peter Krempa <pkrempa@redhat.com>