LU-13672 tune2fs: reset MMP state on error exit

LU-13672 tune2fs: reset MMP state on error exit

If tune2fs cannot perform the requested change, ensure that the MMP
block is reset to the unused state before exiting.  Otherwise, the
filesystem will be left with mmp_seq = EXT4_MMP_SEQ_FSCK set, which
prevents it from being mounted afterward:

    LDISKFS-fs warning (device dm-9): ldiskfs_multi_mount_protect:311:
        fsck is running on the filesystem

Add a test to try some failed tune2fs operations and verify that the
MMP block is left in a clean state afterward.

Change-Id: I3a5acc5875fa2d082a66e751ec4b326ffe3ebbe5
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/38926
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>