improve exception type if failed while waiting for async task

[javeme]

Change-Id: Ifab67a27bc294618bee769f8d22540ab01905111

[codecov]

Codecov Report

Merging #596 into master will increase coverage by 3.51%.
The diff coverage is 37.5%.

@@             Coverage Diff              @@
##             master     #596      +/-   ##
============================================
+ Coverage     66.93%   70.44%   +3.51%     
- Complexity     3332     3458     +126     
============================================
  Files           216      216              
  Lines         16605    16612       +7     
  Branches       2366     2367       +1     
============================================
+ Hits          11114    11702     +588     
+ Misses         4299     3661     -638     
- Partials       1192     1249      +57

Impacted Files	Coverage Δ	Complexity Δ
.../baidu/hugegraph/backend/tx/SchemaTransaction.java	85.27% <37.5%> (-2.62%)	62 <0> (ø)
...c/main/java/com/baidu/hugegraph/HugeException.java	75% <0%> (-25%)	3% <0%> (-1%)
...du/hugegraph/backend/tx/GraphIndexTransaction.java	79.52% <0%> (-0.48%)	146% <0%> (ø)
...hugegraph/backend/serializer/BinarySerializer.java	80.1% <0%> (+0.16%)	102% <0%> (ø)	⬇️
.../baidu/hugegraph/backend/query/ConditionQuery.java	82.15% <0%> (+0.46%)	87% <0%> (+1%)	⬆️
.../backend/store/cassandra/CassandraSessionPool.java	59.79% <0%> (+1.03%)	13% <0%> (ø)	⬇️
...om/baidu/hugegraph/backend/store/BackendTable.java	94% <0%> (+4%)	12% <0%> (ø)	⬇️
...u/hugegraph/backend/store/hbase/HbaseSessions.java	64.72% <0%> (+64.72%)	22% <0%> (+22%)	⬆️
...aidu/hugegraph/backend/store/hbase/HbaseStore.java	72.43% <0%> (+72.43%)	27% <0%> (+27%)	⬆️
.../backend/store/scylladb/ScyllaDBStoreProvider.java	76.59% <0%> (+76.59%)	7% <0%> (+7%)	⬆️
... and 7 more

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[zhoney]

'cause' is exception arg, 'cause.getMessage()' is message arg, so change order of them.

         throw new HugeException("Async task failed with error: %s",
                                 cause, cause.getMessage());

[zhoney]

ditto