LU-1842 quota: define quota records for glb/slv indexes

LU-1842 quota: define quota records for glb/slv indexes

This patch defines lquota_glb_rec & lquota_slv_rec which are the
record which will be used with the global & slave index files.
It also introduces the global quota lu_context_key which will be used
by all quota-level handlers.
The lquota module init/exit function are now defined in lquota_lib.c
which calls the old quota init/exit function for the time being.
Finally, this patch also modifies lquotactl_slv() to collect
enforcement information.

Signed-off-by: Johann Lombardi <johann@whamcloud.com>
Change-Id: I2b261bd8433a5e6bd64c2de2710bca32bf606122
Reviewed-on: http://review.whamcloud.com/3886
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Reviewed-by: Niu Yawei <niu@whamcloud.com>