[tests] allow dev's to view test process output locally

[jrushlow]

Allows developers to set MAKER_TEST_DUMP_OUTPUT=true when running tests to view the raw output of a maker command during testing for local debugging purposes.

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• The value of MAKER_TEST_DUMP_OUTPUT must be the literal true. Values other then the string literal true are ignored.
• This should never be used in CI or when running the entire test suite locally
• It is meant to aid developers working on MakerBundle commands that need to see the actual output sub-process output && error output of maker commands that are executed via MakerTestRunner's runMaker() method.

Usage

MAKER_TEST_DUMP_OUTPUT=true vendor/bin/simple-phpunit --filter MakeVoter