Create scrambled table that has same partition columns as its original table

[dongyoungy]

• 'CREATE SCRAMBLE' will create a scrambled table that has same partition columns as its original table (resolves #303)

[codecov-io]

Codecov Report

Merging #326 into master will increase coverage by 2.47%. The diff coverage is 81.14%.

@@            Coverage Diff             @@
##           master     #326      +/-   ##
==========================================
+ Coverage   68.24%   70.71%   +2.47%     
==========================================
  Files         167      167              
  Lines       11198    11233      +35     
  Branches     1839     1847       +8     
==========================================
+ Hits         7641     7942     +301     
+ Misses       3095     2831     -264     
+ Partials      462      460       -2

Impacted Files	Coverage Δ
.../verdictdb/sqlreader/ScramblingQueryGenerator.java	0% <ø> (ø)	:arrow_up:
...va/org/verdictdb/coordinator/ExecutionContext.java	87.46% <100%> (+16.66%)	:arrow_up:
...ctdb/core/scrambling/CreateScrambledTableNode.java	73.08% <100%> (+0.53%)	:arrow_up:
.../org/verdictdb/core/scrambling/ScramblingNode.java	94.12% <100%> (+0.62%)	:arrow_up:
.../verdictdb/core/sqlobject/CreateScrambleQuery.java	45.46% <45.46%> (+3.46%)	:arrow_up:
.../java/org/verdictdb/connection/JdbcConnection.java	73.88% <80%> (+8.13%)	:arrow_up:
...g/verdictdb/coordinator/ScramblingCoordinator.java	76.38% <84.22%> (+0.94%)	:arrow_up:
...ava/org/verdictdb/metastore/ScrambleMetaStore.java	97.39% <0%> (-1.3%)	:arrow_down:
...a/org/verdictdb/jdbc41/VerdictStreamResultSet.java	8.29% <0%> (-0.26%)	:arrow_down:
.../core/scrambling/FastConvergeScramblingMethod.java	91.08% <0%> (+0.3%)	:arrow_up:
... and 29 more

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[dongyoungy]

For 'partition by list' syntax that we use to implement partitioned tables in Postgres and MySQL, Postgres only supports a single column partition while MySQL can support partition with multiple columns using 'LIST COLUMNS'.

For now, I have made it to throw an exception for Postgres and MySQL when one tries to create a scramble for already-partitioned tables as suggested. This check is done by existing checkIfSupported() method in CreateScrambleQuery.

We may implement multi-column partitioned scrambles for MySQL in the future, but I do not think it is necessary at the moment.

[pyongjoo]

Thanks. Please merge to master whenever you think it's OK.