Improve debugging formatting in Jetty mojos

[jsoref]

When I use hpi:run in a project, I see something like this:

[INFO] Tmp directory = /tmp/jenkinsci/workflow-basic-steps-plugin/target/jetty
[INFO] Web defaults = org/eclipse/jetty/webapp/webdefault.xml
[INFO] Web overrides =  none

There are two spaces between = and none for no apparent reason.

This change replaces the second space followed by a default_message with (+default_message+).