Additional mutant statuses (TIMED_OUT, BUILD_FAILED)

[k3rn31]

Currently, Gremlins supports KILLED, LIVED, NOT_COVERED and RUNNABLE status.
It should also report if the test fails for a timeout or for a build error, so two new statuses should be introduced:

• TIMED_OUT
• BUILD_FAILED

BUILD_FAILED

Should be easy enough to implement: tests failed for a build error have exit code 2 (while test failures have 1). We can simply set the mutation status based on the exit code of the tests.

TIMED_OUT

This is trickier because timed out tests have exit code 1 (same as normal test failures). How can detect if the test has timed out?
I can think of two options:

1. Search the output of the test looking for "panic: test timed out after XXs" string (ugly solution)
2. Do not use the -timeout XXs flag in the test and manage test timeouts outside of the command, using a context with timeout and exec.CommandContext,

Ideas are welcome.

[k3rn31]

NOT VIABLE is a better name than BUILD FAILED, since it remains more generic and can be used for other use cases in the future.