Only print the exception messages for CLI connection issues.

https://issues.jboss.org/browse/WFCORE-133
Let's be consistent with the way the CLI reports errors (after all this is what the issue is about). Have a look at how it's done in CommandContextImpl.handlSafe(...). If you want, you could a new method to org.jboss.as.cli.Util, e.g

String toErrorMessage(Throwable t)

and call it in both cases.