Calculating the test suite duraion from timestamps

[linzhp]

What type of PR is this?
Bug fix

What does this PR do? Why is it needed?
When test cases use t.Parallel(), the duration of a test suite is more than that of the test case with the same name. For example, when we run this test:

func TestParallel(t *testing.T) {
	t.Run("Test 1", func(t *testing.T) {
		time.Sleep(1 * time.Second)
	})

	t.Run("Test 2", func(t *testing.T) {
		t.Parallel()
		time.Sleep(2 * time.Second)
	})
}

The log shows:

=== RUN   TestParallel
=== RUN   TestParallel/Test_1
=== RUN   TestParallel/Test_2
=== PAUSE TestParallel/Test_2
=== CONT  TestParallel/Test_2
--- PASS: TestParallel (1.00s)
    --- PASS: TestParallel/Test_1 (1.00s)
    --- PASS: TestParallel/Test_2 (2.00s)
PASS

TestParallel/Test_2 took 2 seconds, but the test case TestParallel only took 1 second. Apparently, the test suite TestParallel should have taken more than 1 second.

This PR uses the timestamps from JSON events to determine end to end time of a test suite.

[linzhp]

CI failed due to bazelbuild/continuous-integration#2183