Cleaner fix for JBIDE-13599

Based on snjeza's patch but witout hard dependency on dmr, with no
dependency on having properties set in pom (can run tests from the
IDE), more tests and fully functional ${foo,bar:default} syntax as use
in iin jboss.

Adds suport for ${foo}, ${foo,baz}, ${foo:default}, ${foo,baz:default}
for the site url in the discovery url mechanism.