LU-4017 e2fsprogs: clean up codes for adding new quota type

LU-4017 e2fsprogs: clean up codes for adding new quota type

Adding directory/project quota support to ext4 is widely discussed
these days. E2fsprogs has to be updated if we want that new feature.
As a preparation for it, this patch cleans up quota codes of e2fsprogs
so as to make it easier to add new quota type(s).

Signed-off-by: Li Xi <lixi@ddn.com>
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Change-Id: I9d2e669c449c77fe97163fa70c4ff37777e23261
Reviewed-on: http://review.whamcloud.com/15761
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>