LU-16835 tune2fs: fall back to old get/set fs label on error

LU-16835 tune2fs: fall back to old get/set fs label on error

If we fail to get/open the mount point for get/set
fs label ioctl, just fall back to old method and
silence the error messages.

Change-Id: I2ce5c02974540ff0fe883b992d0b510e68f6db26
Fixes: f85b4526f ("tune2fs: implement support for set/get label iocts")
Signed-off-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-on: https://review.whamcloud.com/c/tools/e2fsprogs/+/51073
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>