[split] Var: remove Var.apply; introduce Var.sample

RB_ID=211248
[split] Adds com.twitter.io.exp.VarSource

RB_ID=209842
[split] util: Fix testing all of util with pants

RB_ID=216638
[split] util-core: improve allocation/perf in Offer.choose and Future.select

- Added new method Future.selectIndex providing positional "select"

RB_ID=216278
[split] finagle-core: buffers requests until Var[Addr] is in a ready state

RB_ID=210150
[split] util-core: adds closable.close(Duration)

RB_ID=200369
[split] flaky test in util/FuturePoolSpec

RB_ID=221287
TBR=true
NO-QUEUE=true
[split] fix null error for Flaggable[InetSocketAddress] Handle cases when InetSocketAddress("un.resolveable.name", 1234).getAddress returns null.

RB_ID=220975
[split] [COORD-236] Fix Promise update race when interrupting FuturePool threads.

RB_ID=221309
[split] util-core: adds comment re using FuturePool from java

RB_ID=221855
[split] util and finagle scaladoc warning cleanup

- Add Unidoc support to util, copy-pasting from Finagle
- Use proper Scaladoc tags
- Wiki syntax for text decoration
- String trailing spaces from files we touched
- Fix usage of Scaladoc macro

RB_ID=222977
[split] take -com.twitter.server.serversetZkHosts flag (for tunnelling)

RB_ID=221317
[split] [twitter-context] better Java compatibility

Java usage:
TwitterContext ctx = TwitterContext.acquire(Permit.get())

RB_ID=225381
[split] finagle-core: tests default client

RB_ID=223607
[split] [util-zk-common] update pom com.twitter.common.zookeeper dependencies

RB_ID=227013
[split] release util version 6.8.0

RB_ID=230117
TBR=true
[split] Higher fidelity addrs from ZK We do the best we can with the current server set implementation. A new one is coming soon; this should be enough to limp along until then.

* This also sneaks in names for uses of the legacy
Resolver.resolve interfaces by creating a type of
Group which is little more than a container for a Name.

* Also caches resolutions down to env/role/job.

* Phrases stabilizing group in terms of Addrs.

Note: the goal with StabilizingAddr is to replicate
exactly what StabilizingGroup did. I don???t want to
change it. Something new and simpler is coming soon
enough. StabilizingAddr is transient.

RB_ID=219996
[split] util-core: Break apart interruptible FuturePool for java backcompat

RB_ID=231429
[split] Release util version 6.8.1

RB_ID=232807
TBR=true
[split] Create script to test all of CSL with pants This also fixes a few issues when testing with pants.

RB_ID=226911