The following log statement is logged (twice?) when stopping (or restarting) Tomcat 8.x using Cargo:
Erik found out that these annoying log messages (StandardServer.await: Invalid command '' received) originates from code in the method AbstractLocalContainer#waitForCompletion. In particular the following, and rather naive (but presumably harmless), line: https://github.com/codehaus-cargo/cargo/blob/master/core/api/container/src/main/java/org/codehaus/cargo/container/spi/AbstractLocalContainer.java#L361
The Tomcat shutdown port is in fact a property ending with .port (cargo.rmi.port), which makes Cargo issue a request to the shutdown port with no "command" (it just try to connect to port). This happens, even several times, before the correct shutdown command (issued by Cargo) is received and processed by Tomcat - which results in these annoying log messages.