Try to recover corrupted ext4 /data with backup superblock

If the superblock of /data is corrupted, fs_mgr would skip check_fs.
But, e2fsck actually may reference backup superblock to recover
the filesystem. This fix gives fs_mgr second chance to fix corrupted
ext4 /data.

Bug: 156200421
Test: boot with corrupted ext4 superblock

Signed-off-by: Randall Huang <huangrandall@google.com>
Change-Id: Ia39af3340c0e241f62557b7c2cc8b800443342f9