tools: make sure "veyron test ..." returns a zero status only if all tests the command executes pass
tools: make sure "veyron test ..." returns a zero status only if all
tests the command executes pass

Change-Id: I757322a31cf567475c410fcdf7b2f9c0e0e30533

vanadium/go.devtools,vanadium/go.devtools,vanadium/go.devtools