Use a concurrency-safe writer in runWithTimeout to avoid data races
on the bytes.Buffer passed in during tests.
Bug: 181095653
Fixes: 187149270
Test: Test_runWithTimeout
Test: go test -race ./cmd/run_with_timeout
Change-Id: I57a889765cb9ee7b42983f0906313e0c2d1e414e
Add a command that can be used to wrap actions with a timeout, and
optionally run an extra debugging command on timeout.
Bug: 181095653
Test: run_with_timeout_test.go
Change-Id: I91df5c3fb5277968717815a4ad4612113766dab1