This CL changes the last line displayed after the program was run
to display more details on what happened.
If the program cannot be built,
the last message is "Go build failed".
If the program has tests,
the last message is "All tests passed" in case of success.
Otherwise it is "N tests failed".
If the program has exited with non-zero code,
the exit message is postfixed with the code.
This CL adds output for timed out programs.
This CL is prerequisite for the backend change in CL 141478.
Dockerfile in playground repo has to be updated to include this CL.
Updates golang/go#10590
Updates golang/go#25454
Change-Id: Ie0a51b0729c574d2508a4a1b89f629def1d79fd6
Reviewed-on: https://go-review.googlesource.com/c/141477
Reviewed-by: Andrew Bonventre <andybons@golang.org>
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