Support to detect connection before using if needed

[Linary]

Fix #556

Change-Id: I622e285f812098d601061f2515d70629f1e07d88

[codecov]

Codecov Report

Merging #562 into master will decrease coverage by 0.48%.
The diff coverage is 80.32%.

@@             Coverage Diff              @@
##             master     #562      +/-   ##
============================================
- Coverage     70.22%   69.74%   -0.49%     
- Complexity     3418     3442      +24     
============================================
  Files           216      216              
  Lines         16465    16630     +165     
  Branches       2351     2378      +27     
============================================
+ Hits          11563    11599      +36     
- Misses         3646     3789     +143     
+ Partials       1256     1242      -14

Impacted Files	Coverage Δ	Complexity Δ
...h/backend/store/rocksdbsst/RocksDBSstSessions.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...aidu/hugegraph/backend/store/mysql/MysqlStore.java	73.41% <0%> (ø)	34 <0> (ø)	⬇️
...raph/backend/store/rocksdb/RocksDBStdSessions.java	69.65% <100%> (+0.42%)	24 <1> (+1)	⬆️
...gegraph/backend/store/rocksdb/RocksDBSessions.java	100% <100%> (ø)	1 <1> (ø)	⬇️
...aidu/hugegraph/backend/store/hbase/HbaseStore.java	72.43% <100%> (+1.65%)	27 <0> (+1)	⬆️
...egraph/backend/store/cassandra/CassandraStore.java	65.15% <100%> (+1.41%)	45 <0> (+3)	⬆️
.../backend/store/cassandra/CassandraSessionPool.java	58.76% <100%> (+0.42%)	13 <1> (ø)	⬇️
...u/hugegraph/backend/store/hbase/HbaseSessions.java	64.72% <100%> (+0.13%)	22 <2> (ø)	⬇️
...n/java/com/baidu/hugegraph/config/CoreOptions.java	98.64% <100%> (+0.05%)	2 <0> (ø)	⬇️
...u/hugegraph/backend/store/mysql/MysqlSessions.java	73.15% <16.66%> (+2.24%)	24 <1> (+6)	⬆️
... and 23 more

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