JBDS-3066 : ensure ide-config.properties loads from org.jboss.tools.foundation.core when offline

The heart of the fix is https://github.com/fbricon/jbosstools-base/compare/jbosstools:jbosstools-4.2.0.Beta2x...JBDS-3066-4.2.0.Beta2x?expand=1#diff-590f1aab49f4c8100293e01ed2c64a6aR185

The rest of the changes is for unit testing