expand jetty properties when generating dry-run command line

[lachlan-roberts]

When using --dry-run, the command line printed was not resolving jetty properties.

For example using logging-jetty adds ${jetty.home.uri}/lib/logging/ to server classes.

However this is never resolved with the value of the jetty.home.uri property, and this is what is what ends up in server classes of the webapp when Jetty is started:

|  |     +> Serverclasses XWiki@c05fddc size=22
|  |     |  +> ${jetty.home.uri}/lib/logging/

this results in the ServiceConfigurationError seen in jetty/jetty.docker#118.

[joakime]

Simple enough.