Make parsertests --quiet truly quiet.

* Create defaultLogLevels in Logger (initially "error",
  "warning", "fatal") and also a changeLogLevels function
  that alters the defaultLogLevels.

* If the "quiet" flag is set in parserTests, the logger's
  defaultLogLevels are changed to only "error" and "fatal",
  so the parserTests generate less noise.

Change-Id: I4ba5890cefa79c4c7ca1f67be3c146e7188e471d