generic/496: ext4 and xfs supports swapon on fallocated file

generic/496: ext4 and xfs supports swapon on fallocated file

ext4, xfs should not fail swapon on fallocated file. Currently if this
fails the fstst was not returning a failure. Fix those for given
filesystems (for now added ext4/xfs).
There were some regressions which went unnoticed due to this in ext4
tree, which later got fixed as part of this patch [1]

[1]: https://patchwork.ozlabs.org/patch/1357275

Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>