Bug 995027 logging - add traces to figure out whether uninit was called and where it got stuck, r=gfritzsche

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extra : rebase_source : 6c2e5dcce364bbce746a11b4e8841283656162c2
Bug 997188 - Handle the experiments.manifest.uri pref correctly so so that it don't ping out to telemetry-experiments.cdn.mozilla.net by default or enable experiment code in the tests. This should also fix bug 994686. r=irving/gfritzsche