overlay/060: Use falloc to make sure a meta copy file got copied up

overlay/060: Use falloc to make sure a meta copy file got copied up

Overlayfs might copy up data of file on first write of file (and
not necessarily upon open of file). So call falloc file opened
with O_RDWR and after that data must have been copied up.

[Eryu: add _require_xfs_io_command "falloc" to make sure underlying
fs have fallocate(2) support]

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>