Use actual test duration to populate the `time` attribute in reports.

Use the test duration value supplied by QUnit to populate the `time` attribute in the report.

* `grunt-contrib-qunit` 0.5.2 includes a duration param in the `qunit.testDone` event.
* Modified XmlReporter to convert the value from ms to a `X.yy` string formatted in seconds.
* Enforce a minimum time of `0.01` seconds for each test case
* Sum all tests to provide the total duration of each testsuite.
* Modify tests to provide fuzzy matching around times - this ensures that small variations in timing don't fail the suite.