finagle-core: canonical name for per host stats

[fuCtor]

Issue #918

Problem: With DNS balancing per host stats are collapsing in single branch.

Solution: Use canonical host name in stats receiver scope.

[CLAassistant]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

Merging #919 (ff4dd62) into develop (81dbd79) will increase coverage by 11.23%. The diff coverage is 70.00%.

@@             Coverage Diff              @@
##           develop     #919       +/-   ##
============================================
+ Coverage    63.65%   74.88%   +11.23%     
============================================
  Files          948      912       -36     
  Lines        32199    26710     -5489     
  Branches      2085     1606      -479     
============================================
- Hits         20495    20002      -493     
+ Misses       11704     6708     -4996     

Impacted Files	Coverage Δ
...ter/finagle/loadbalancer/LoadBalancerFactory.scala	83.09% <70.00%> (+3.24%)	:arrow_up:
...tter/finagle/dispatch/SerialClientDispatcher.scala	83.33% <0.00%> (-16.67%)	:arrow_down:
...main/scala/com/twitter/finagle/stats/Metrics.scala	80.95% <0.00%> (-2.39%)	:arrow_down:
...om/twitter/finagle/dispatch/ServerDispatcher.scala	82.97% <0.00%> (-2.13%)	:arrow_down:
...inagle/http2/transport/server/H2ServerFilter.scala	82.69% <0.00%> (-1.93%)	:arrow_down:
...com/twitter/finagle/netty4/ConnectionBuilder.scala	75.80% <0.00%> (-1.62%)	:arrow_down:
...ala/com/twitter/finagle/serverset2/ZkSession.scala	81.29% <0.00%> (-0.59%)	:arrow_down:
...ift/scribe/thriftscala/Scribe$FinagleService.scala
...rift/scribe/thriftscala/Scribe$FinagleClient.scala
...tter/finagle/thrift/thriftscala/UpgradeReply.scala
... and 40 more

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[yufangong]

Merged in https://github.com/twitter/finagle/commit/cde98b358a92d8dd722767fd08c6e38ba00bd37b Thanks for the PR!