Order tests in tool_test_output.html when --failed supplied

It took me awhile today to realize that when you have multiple tests failing and you run `planemo test --failed`, the order of the tests in the `tool_test_output.html` file appears to be random and does not reflect the order they occur in the tool's xml file. The names of the failed tests have the correct number, which corresponds to the order of their occurrence in the xml.

So this is a feature request to order the occurrences of the test results in `tool_test_output.html`.

I had 4 failing tests (5-8) and their order in the results were 7, 8, 5, 6.