generic/071: check if fs supports fallocate KEEP_SIZE flag

So that the test is skipped for filesystems that don't support it
instead of failing (like NFS 4.2 for example).

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>
1 file changed