Stack dumps not produced from timed out go-tests

[azdagron]

When a service_test wrapping a go_test times out, it kills the go test indirectly via a context cancellation on CommandContext, inhibiting the go test from dumping useful stack traces to stderr.

It would be really nice to have those stack traces available.

Off the cuff solutions:

1. Override the TEST_TIMEOUT envvar set by bazel by some reduced margin so that the go test hits its own natural timeout and exits with stack traces
2. kill the go test process via SIGQUIT (e.g. override the Cancel func on the exec.Command to send a different signal), which also produces stack traces

(1) would work with any test written for bazel test (i.e. those that honor TEST_TIMEOUT)