Add replication setting for NetworkTopologyStrategy of Cassandra

[zhoney]

Change-Id: Idc10d03f1b23daf9bf73bc2e392fde9971fc36d9

[codecov]

Codecov Report

Merging #448 into master will increase coverage by 0.03%.
The diff coverage is 70.58%.

@@             Coverage Diff              @@
##             master     #448      +/-   ##
============================================
+ Coverage     70.15%   70.18%   +0.03%     
- Complexity     3281     3286       +5     
============================================
  Files           208      208              
  Lines         16082    16097      +15     
  Branches       2310     2314       +4     
============================================
+ Hits          11282    11298      +16     
+ Misses         3547     3546       -1     
  Partials       1253     1253

Impacted Files	Coverage Δ	Complexity Δ
.../main/java/com/baidu/hugegraph/cmd/ConfDumper.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...raph/backend/store/cassandra/CassandraOptions.java	100% <100%> (ø)	3 <0> (ø)	⬇️
.../hugegraph/backend/store/rocksdb/RocksDBStore.java	58.46% <14.28%> (+0.22%)	41 <0> (ø)	⬇️
...egraph/backend/store/cassandra/CassandraStore.java	64.5% <86.95%> (+1.23%)	42 <5> (+5)	⬆️
...ain/java/com/baidu/hugegraph/task/TaskManager.java	60.86% <0%> (-4.35%)	10% <0%> (-1%)
...du/hugegraph/backend/tx/GraphIndexTransaction.java	79.84% <0%> (+0.47%)	145% <0%> (ø)	⬇️
...n/java/com/baidu/hugegraph/task/TaskScheduler.java	52.69% <0%> (+1.24%)	27% <0%> (+1%)	⬆️

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