Changes to use Helix aggregated view cluster

[Arun-LinkedIn]

This PR contains changes needed to use Helix aggregated view cluster (which should be available locally in each data center) for getting global cluster information instead of fetching individual data center information from each of the helix/ZK clusters.

This should speed up the start time frontends and servers since cluster information would be fetched from local Zookeeper servers instead of fetching from multiple remote Zookeepers.

[codecov-commenter]

Codecov Report

Base: 73.00% // Head: 72.99% // Decreases project coverage by -0.00% :warning:

Coverage data is based on head (a50b508) compared to base (0f6bfa7). Patch coverage: 37.16% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2248      +/-   ##
============================================
- Coverage     73.00%   72.99%   -0.01%     
- Complexity    10316    10402      +86     
============================================
  Files           747      753       +6     
  Lines         56853    57592     +739     
  Branches       6997     7081      +84     
============================================
+ Hits          41503    42039     +536     
- Misses        13092    13237     +145     
- Partials       2258     2316      +58     

Impacted Files	Coverage Δ
...bry/clustermap/HelixAggregatedViewClusterInfo.java	0.00% <0.00%> (ø)
...stermap/HelixAggregatedViewClusterInitializer.java	0.00% <0.00%> (ø)
...m/github/ambry/clustermap/HelixClusterManager.java	84.73% <60.71%> (-2.55%)	:arrow_down:
...java/com/github/ambry/config/ClusterMapConfig.java	100.00% <100.00%> (ø)
...b/ambry/clustermap/HelixDatacenterInitializer.java	96.42% <100.00%> (ø)
...ambry/messageformat/MessageSievingInputStream.java	85.95% <0.00%> (-10.96%)	:arrow_down:
.../java/com/github/ambry/router/RouterException.java	43.75% <0.00%> (-6.25%)	:arrow_down:
...hub/ambry/protocol/CatchupStatusAdminResponse.java	81.25% <0.00%> (-6.25%)	:arrow_down:
...a/com/github/ambry/network/SSLBlockingChannel.java	75.67% <0.00%> (-5.41%)	:arrow_down:
.../java/com/github/ambry/protocol/AmbryRequests.java	78.01% <0.00%> (-3.23%)	:arrow_down:
... and 48 more

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