LU-2049 grant: Fix grant interop with pre-GRANT_PARAM clients

LU-2049 grant: Fix grant interop with pre-GRANT_PARAM clients

Fix a performance regression with pre-GRANT_PARAM clients.
This patch brings the grant allocation logic back into line with how
servers prior to GRANT_PARAM support allocated grant space.

Test-Parameters: clientdistro=el6.6 clientjob=lustre-b2_7 clientbuildno=29 testlist=sanity-quota mdscount=1 mdtcount=1 ostcount=2 envdefinitions=SANITY_QUOTA_EXCEPT="36"
Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: I63fd5b91b499936b74d2dd21c1215e0b006af085
Reviewed-on: https://review.whamcloud.com/25853
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>