support rocksdb multi-get

[javeme]

Change-Id: I5e3f67e46c29bacd55794547f08a63d8832020fb

[codecov]

Codecov Report

Merging #1682 (9388b5f) into master (83180fb) will increase coverage by 2.35%.
The diff coverage is 66.03%.

@@             Coverage Diff              @@
##             master    #1682      +/-   ##
============================================
+ Coverage     64.40%   66.76%   +2.35%     
- Complexity     6897     7055     +158     
============================================
  Files           421      420       -1     
  Lines         34675    34714      +39     
  Branches       4803     4814      +11     
============================================
+ Hits          22334    23178     +844     
+ Misses        10058     9195     -863     
- Partials       2283     2341      +58     

Impacted Files	Coverage Δ
...gegraph/backend/store/rocksdb/RocksDBSessions.java	100.00% <ø> (ø)
...h/backend/store/rocksdbsst/RocksDBSstSessions.java	46.09% <0.00%> (-0.74%)	⬇️
.../hugegraph/backend/store/rocksdb/RocksDBTable.java	68.08% <41.66%> (-2.91%)	⬇️
...raph/backend/store/rocksdb/RocksDBStdSessions.java	74.37% <76.31%> (+0.08%)	⬆️
...hugegraph/backend/store/rocksdb/RocksDBTables.java	73.37% <100.00%> (+0.17%)	⬆️
...om/baidu/hugegraph/backend/query/QueryResults.java	70.09% <0.00%> (-1.34%)	⬇️
.../com/baidu/hugegraph/type/define/SchemaStatus.java	80.00% <0.00%> (-0.96%)	⬇️
...java/com/baidu/hugegraph/schema/SchemaElement.java	77.14% <0.00%> (-0.33%)	⬇️
...c/main/java/com/baidu/hugegraph/util/LockUtil.java	84.93% <0.00%> (-0.21%)	⬇️
...in/java/com/baidu/hugegraph/StandardHugeGraph.java	68.47% <0.00%> (-0.20%)	⬇️
... and 37 more

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