LUDOC-328 tbf: add UID/GID based policy to NRS-TBF section

LUDOC-328 tbf: add UID/GID based policy to NRS-TBF section

Update NRS-TBF policy section to reflect UID/GID based TBF
policy:
- format: uid={uid} or gid={gid} or uid={uid}&gid={gid}
- Lustre-commit: e0cdde123c14729a340cf937cf9580be7c9dd9c1
- Lustre-change: http://review.whamcloud.com/27608

Change-Id: I49302f35bb6fae3de9410a8b84940aa8df7b0ca7
Signed-off-by: Emoly Liu <emoly.liu@intel.com>
Reviewed-on: https://review.whamcloud.com/31769
Tested-by: Jenkins
Reviewed-by: Joseph Gmitter <joseph.gmitter@intel.com>