Update gulp `test` task to fail on test errors

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The CI process for this PR will fail because tests are failing. But before this PR, these failing tests resulted in green builds which not correct. The fixes in this PR return any errors from running tests to the calling process and return non-zero return codes in the case of failing tests.

References #417

ngOfficeUIFabric / ng-officeuifabric

Update gulp `test` task to fail on test errors #418