[split] exclude CancelledRequestException and CancelledConectionException or cache client failure accrual

RB_ID=188141
[split] finagle-core: improve HeapBalancer req distribution when N=2

With 2 nodes and a stream of sequential requests,
the HeapBalancer would always choose the same node

Signed-off-by: Steve Gury <stevegury@twitter.com>

RB_ID=187179
[split] only need one set of parentheses

RB_ID=185731
[split] retryingfilter specs -> scalatest

RB_ID=184933
[split] Group: communicate via Var[Set[T]]

This will make it simpler to unify Groups with Wily.
I'm hoping to deprecate Groups entirely in favor of
Var[Addr] as per Wily, but the type may remain as a
facade.

RB_ID=183145
[split] Finagle: upgrade Netty to 3.7.0.Final

RB_ID=184661
[split] finagle-core: lets the number of cores be specified at the command line

RB_ID=183001
[split] Provide generic request contexts.

/**
 * A context is a piece of serializable metadata managed by a
 * registered handler. Protocol implementations may enumerate current
 * contexts to associate with outgoing messages; incoming contexts
 * are handled.
 *
 * Each context type is associated with a key. Keys with no
 * registered handlers are assigned a pass-thru handler: they are
 * uninterpreted, but are propagated across requests.
 *
 * Context handlers implement ContextHandler and are loaded via
 * the Java service loader mechanism.
 */

RB_ID=188653
[split] ZK based cache node group implementation

RB_ID=181107
[split] Tagging Zookeeper tests as flaky

RB_ID=191207
[split] ensure FIFO ordering when delivering updates to stabilizing group

RB_ID=191623
[split] better interface for RetryPolicy

RB_ID=182536
[split] csl: improves csl release process

RB_ID=190841
[split] mark additional flaky test

RB_ID=191931
[split] Var: move to core util, add Var.unapply

RB_ID=190993
[split] SPNEGO http auth (for Kerberos) in finagle with an example implementation for internal services

RB_ID=187389
[split] finagle-core: fix sourcing for SourcedExceptions

RB_ID=186115
[split] read key remapping config off from zk

RB_ID=192277
[split] finagle-core: added UnwritableChannel stat to ChannelStatsHandler

RB_ID=193245
[split] bump scrooge to 3.9.1-SNAPSHOT

RB_ID=193745
TBR=true