tests: metrics: Improve detection of which runtime was tested

[grahamwhaley]

The metrics result reporting script tests/lib/send_resulst.sh.in tries to work out which runtime is being tested so it can extract version and/or tag information for logging - but, it could be smarter. Really it could do with either/or extracting the information from the environment (e.g. Docker), or the test itself could/should pass in the information (as potentially only the test may know which actual runtime it was testing).