generic: file fsync after unlink and inode eviction

generic: file fsync after unlink and inode eviction

Test that if we remove one hard link from an inode, evict the inode,
fsync the inode, power fail and then mount the filesystem, the hard
link we removed does not exists anymore and the filesystem metadata
is in a consistent state.

This test is motivated by an issue found on btrfs, and on an unpatched
btrfs it fails with:

  FSTYP         -- btrfs
  PLATFORM      -- Linux/x86_64 debian3 4.1.0-rc6-btrfs-next-11+
  MKFS_OPTIONS  -- /dev/sdc
  MOUNT_OPTIONS -- /dev/sdc /home/fdmanana/btrfs-tests/scratch_1

  generic/098 4s ... - output mismatch (see .../generic/098.out.bad)
    --- tests/generic/098.out	2015-07-23 18:01:12.616175932 +0100
    +++ .../generic/098.out.bad	2015-07-23 18:04:58.924138308 +0100
    @@ -1,3 +1,6 @@
     QA output created by 098
     Entries in testdir:
    +bar
     foo
    +rm: cannot remove '.../testdir/foo': Stale file handle
    +rmdir: failed to remove '.../scratch_1/testdir': Directory not empty
    ...
  _check_btrfs_filesystem: filesystem on /dev/sdc is inconsistent ...
  (...)

  $ cat /home/fdmanana/git/hub/xfstests/results/generic/098.full
  (...)
  checking fs roots
  root 5 inode 258 errors 2001, no inode item, link count wrong
   unresolved ref dir 257 index 0 namelen 3 name foo filetype 1 errors 6,\
       no dir index, no inode ref
   unresolved ref dir 257 index 3 namelen 3 name bar filetype 1 errors 5,\
       no dir item, no inode ref
  (...)

Tested against ext3/4, xfs, f2fs and reiserfs.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>