Allow NettyPerfClient to connect multiple frontends

[jsjtzyy]

1. log response based on response code range rather than single response
   code value.
2. allow perfClient to connect multiple frontends.

[codecov-io]

Codecov Report

Merging #1217 into master will decrease coverage by 0.01%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             master    #1217      +/-   ##
============================================
- Coverage     69.67%   69.66%   -0.02%     
- Complexity     5476     5478       +2     
============================================
  Files           431      431              
  Lines         33554    33573      +19     
  Branches       4258     4262       +4     
============================================
+ Hits          23380    23387       +7     
- Misses         9000     9017      +17     
+ Partials       1174     1169       -5

Impacted Files	Coverage Δ	Complexity Δ
....github.ambry/tools/perf/rest/NettyPerfClient.java	0% <0%> (ø)	0 <0> (ø)	⬇️
.../main/java/com.github.ambry.router/EncryptJob.java	92.1% <0%> (-5.27%)	4% <0%> (-1%)
...b.ambry.network/BlockingChannelConnectionPool.java	70.42% <0%> (-1.88%)	8% <0%> (ø)
...va/com.github.ambry.replication/ReplicaThread.java	74.62% <0%> (-0.19%)	66% <0%> (-1%)
...in/java/com.github.ambry.store/BlobStoreStats.java	71.13% <0%> (ø)	103% <0%> (-1%)	⬇️
...java/com.github.ambry.network/SSLTransmission.java	69.74% <0%> (+0.31%)	69% <0%> (+1%)	⬆️
...ain/java/com.github.ambry.router/PutOperation.java	90.6% <0%> (+0.35%)	110% <0%> (+2%)	⬆️
....github.ambry.clustermap/StaticClusterManager.java	74.04% <0%> (+1.7%)	83% <0%> (+1%)	⬆️
...github.ambry.rest/AsyncRequestResponseHandler.java	90.87% <0%> (+2.28%)	23% <0%> (ø)	⬇️

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[zzmao]

Minor: Use 'protected' to be more strict?

[zzmao]

Please ignore this. Looks good.

[zzmao]

LGTM.