generic: check inode metadata on f{data}sync after power-cut

generic: check inode metadata on f{data}sync after power-cut

This patch adds case to test fsync and fdatasync with power-cuts.

The rule to check is:
1) fsync should guarantee all the inode metadata after power-cut,
2) fdatasync should guarantee i_size and i_blocks at least after
   power-cut.

Note that, in XFS, it allocates more blocks when doing writes, so it
should close the file before fsync in order to get actual i_blocks
after power-cut.  Or, it needs to do truncate the file with a
specific size to turn it off at the beginning.

Suggested-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>