LU-3558 ptlrpc: Add the NRS TBF policy

LU-3558 ptlrpc: Add the NRS TBF policy

The TBF (Token Bucket Filter) policy schedules and throttles all
types of RPCs for traffic control purposes. It divides RPCs into
different types according to their NIDs or job IDs, and enforces
a RPC rate limit on every type. The handling of a RPC will be delayed
until there are enough tokens for the type. Different types are
scheduled according to their deadlines, so that none of them will be
starving even though the service does not have the ability to satisfy
all the RPC rate requirments of types. The RPCs with the the same
types are queued in a FIFO manner.

Signed-off-by: Li Xi <lixi@ddn.com>
Change-Id: I3f73dfbfb451cc44dfe5e0a575ec7ab5b90ac47e
Reviewed-on: http://review.whamcloud.com/6901
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Tested-by: Oleg Drokin <oleg.drokin@intel.com>