[REEF-1535] Fix .\bin\runtests.ps1 and add -Yarn command line flag to it.
[REEF-1535] Fix .\bin\runtests.ps1 and add -Yarn command line flag to it.

   * Use the new cmdlet name `SubmitYarnApplication`
   * Add new command line parameter `-Yarn`
   * Disable positional binding for cmdlet parameters

JIRA: [REEF-1535](https://issues.apache.org/jira/browse/REEF-1535) closes

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