When --debug is enabled, the embedded process shouldn't be forked

To get all traces (we are missing the ones that are printed by JBoss Logging by the embedded server), the embedded server must run inside the Prospero process and benefit from the JBoss Log Manager configuration.
The line that should be conditioned by the debug mode: https://github.com/wildfly/prospero/blob/main/prospero-common/src/main/java/org/wildfly/prospero/galleon/GalleonUtils.java#L82