CommandService implementations swallowing exceptions

Currently, implementations of org.jboss.arquillian.container.test.spi.command.CommandService like JMXCommandService, ServletCommandService and LocalCommandService are swallowing exceptions in the way they simply return result of a Command even if it's a text of an exception. They should rethrow it instead.

With the current behavior callers of the executors like org.jboss.arquillian.container.test.impl.client.deployment.ContainerDeployer are not aware of any exception and do not show any warning/error message even if the call failed.