test: Make maxBuilds a constant

Signed-off-by: Lewis Marshall <lewis@lmars.net>
test: Add the start time to the build log

Signed-off-by: Lewis Marshall <lewis@lmars.net>
test: Drop the Event channel capacity

Signed-off-by: Lewis Marshall <lewis@lmars.net>
Merge pull request #503 from flynn/test-runner-updates

Test runner updates