tbb-testsuite: fix the navigation-timing, performance-observer, resource-timing, user-timing tests

The navigation-timing test is currently failing with the following error:

test_navigation-timing.py test_navigation-timing.Test.test_navigation_timing
SUITE-END | took 0s
Using workspace for temporary data: "/home/user/tbb-testsuite/reports/r/aXFkPjw0CG/results-tor-browser-linux64-8.0a9_es-ES.tar.xz/navigation-timing_ws"
mozversion application_buildid: 20180204020101
mozversion application_display_name: Tor Browser
mozversion application_id: {ec8030f7-c20a-464f-9b0e-13a3a9e97384}
mozversion application_name: Firefox
mozversion application_remotingname: firefox
mozversion application_vendor: Mozilla
mozversion application_version: 60.1.0
mozversion platform_buildid: 20180204020101
mozversion platform_version: 60.1.0
Application command: /home/user/tbb-testsuite/tmp/w2gSJZPwUj/tor-browser_es-ES/Browser/ff_wrapper -no-remote -marionette -profile /home/user/tbb-testsuite/reports/r/aXFkPjw0CG/results-tor-browser-linux64-8.0a9_es-ES.tar.xz/navigation-timing_ws/profile.default-1534249749
Profile path is /home/user/tbb-testsuite/reports/r/aXFkPjw0CG/results-tor-browser-linux64-8.0a9_es-ES.tar.xz/navigation-timing_ws/profile.default-1534249749
Starting fixture servers
Fixture server listening on http://127.0.0.1:35413/
Fixture server listening on https://127.0.0.1:32829/
e10s is enabled
mozversion application_buildid: 20180204020101
mozversion application_display_name: Tor Browser
mozversion application_id: {ec8030f7-c20a-464f-9b0e-13a3a9e97384}
mozversion application_name: Firefox
mozversion application_remotingname: firefox
mozversion application_vendor: Mozilla
mozversion application_version: 60.1.0
mozversion platform_buildid: 20180204020101
mozversion platform_version: 60.1.0
SUITE-START | Running 1 tests
TEST-START | test_navigation-timing.py Test.test_navigation_timing
Failed to gather test failure debug: 
stacktrace:
        WebDriverError@chrome://marionette/content/error.js:178:5
        UnexpectedAlertOpenError@chrome://marionette/content/error.js:507:5
        assert.that/<@chrome://marionette/content/assert.js:405:13
        assert.noUserPrompt@chrome://marionette/content/assert.js:178:3
        GeckoDriver.prototype._assertAndDismissModal@chrome://marionette/content/driver.js:3203:5
        GeckoDriver.prototype.getPageSource@chrome://marionette/content/driver.js:1154:3
        despatch@chrome://marionette/content/server.js:293:20
        execute@chrome://marionette/content/server.js:267:11
        onPacket/<@chrome://marionette/content/server.js:242:15
        onPacket@chrome://marionette/content/server.js:241:8
        _onJSONObjectReady/<@chrome://marionette/content/transport.js:500:9
        openModalWindow@jar:file:///home/user/tbb-testsuite/tmp/w2gSJZPwUj/tor-browser_es-ES/Browser/omni.ja!/components/nsPrompter.js:353:5
        openPrompt@jar:file:///home/user/tbb-testsuite/tmp/w2gSJZPwUj/tor-browser_es-ES/Browser/omni.ja!/components/nsPrompter.js:563:9
        confirmEx@jar:file:///home/user/tbb-testsuite/tmp/w2gSJZPwUj/tor-browser_es-ES/Browser/omni.ja!/components/nsPrompter.js:704:9
        confirmEx@jar:file:///home/user/tbb-testsuite/tmp/w2gSJZPwUj/tor-browser_es-ES/Browser/omni.ja!/components/nsPrompter.js:74:16
        _promptForLanguagePreference@resource://gre/modules/LanguagePrompt.jsm:177:20
        _handleHttpOnModifyRequest@resource://gre/modules/LanguagePrompt.jsm:156:5
        observe@resource://gre/modules/LanguagePrompt.jsm:47:9

TEST-UNEXPECTED-FAIL | test_navigation-timing.py Test.test_navigation_timing | AssertionError: secureConnectionStart != None
Traceback (most recent call last):
  File "/home/user/tbb-testsuite/virtualenv-marionette-4.3.0/local/lib/python2.7/site-packages/marionette_harness-4.3.0-py2.7.egg/marionette_harness/marionette_test/testcases.py", line 156, in run
    testMethod()
  File "/home/user/tbb-testsuite/marionette/tor_browser_tests/test_navigation-timing.py", line 52, in test_navigation_timing
    script_args=[name, val]), msg=err_msg)
TEST-INFO took 451ms

SUMMARY
-------
passed: 0
failed: 1
todo: 0

FAILED TESTS
-------
test_navigation-timing.py test_navigation-timing.Test.test_navigation_timing
SUITE-END | took 0s