fix #121 DataSourceProcessor and DataSinkProcessor default parallelism

[darionyaphet]

Set DataSourceProcessor and DataSinkProcessor's default parallelism value to 1.

When user startup a processor could don't set parallelism .

GEARPUMP-121

[whjiang]

+1.

[manuzhang]

+0. I think users should be aware of the parallelism of processors to run and I don't see the benefit this change brings. Meanwhile, it's inconsistent with the Processor API now.

[darionyaphet]

@manuzhang When I using some processors to build a DAG , it's just to describe how to process the input stream , parallelism is the attribute of this processor . It should have a default value and one is suitable . thank you for you reply :)

[manuzhang]

@darionyaphet IMO, users should know and take care of their parallelism so we'd better it explicit. They are free to add another layer with default value which make sense for their applications but we'd better assume nothing for them.

[huafengw]

Hi, @darionyaphet please rebase your pr and I will merge it.

[codecov-io]

Current coverage is 62.40%

Merging #13 into master will decrease coverage by 1.55%

1. 2 files (not in diff) in ...rpump/cluster/master were modified. more
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2. 1 files (not in diff) in ...che/gearpump/cluster were modified. more
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3. 1 files (not in diff) in .../org/apache/gearpump were modified. more
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4. 2 files (not in diff) in ...apache/gearpump/util were modified. more
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5. 2 files (not in diff) in ...rpump/cluster/client were modified. more
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6. 2 files (not in diff) in ...che/gearpump/cluster were modified. more
7. File ...ntStoreFactory.scala (not in diff) was modified. more
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8. File ...cutor/Executor.scala (not in diff) was modified. more
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- Hits           3805       3713    -92   
- Misses         2145       2237    +92   
  Partials          0          0          

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