MDL-61689 phpunit: Be stricter about output during unit tests

This change also add fail-on-risky to travis to help pick these up, and
verbosity too.

We only fail on risky during Travis and not during normal output because
developers may want to debug tests.

.travis.yml

@@ -249,7 +249,7 @@ script:
     - >
       if [ "$TASK" = 'PHPUNIT' ];
       then
-        vendor/bin/phpunit;
+        vendor/bin/phpunit --fail-on-risky --disallow-test-output --verbose;
       fi
 
     - >

phpunit.xml.dist

@@ -13,6 +13,7 @@
         stopOnFailure="false"
         stopOnIncomplete="false"
         stopOnSkipped="false"
+        beStrictAboutOutputDuringTests="true"
         printerClass="Hint_ResultPrinter"
         testSuiteLoaderClass="phpunit_autoloader"
         >