report start and end time of test execution

[Martin Leucht]

[Issue now tracked at https://github.com/nunit/nunit-framework/issues/31]

The result XML should also contain the start and end times of a test execution. This is useful to match additional log data from external sources to failing tests, especially when executing long-running tests like system or user acceptance tests or tests that are executed unattended.

Proposed solution:
- add "start"/"starttime" and "end"/"endtime" attributes to "test-case" and "test-suite" elements containing the appropriate time strings used for
- rename the "time" attribute to "duration" to avoid confusion (I know, this is breaking compatibility...)
- this solution may be conflicting with #1072379

[Charlie Poole (charlie.poole)]

This is a reasonable request for nunit 3.0 but breaks the standard format for nunit v2.

[Charlie Poole (charlie.poole)]

We'll add at least the start time and rename elapsed time to duration for the NUnit 3 format. If you use nunit 2 compatible output, then of course the old format will be used.