Fix OPENDJ-1079: OpenDJ UpgradeCli adds HTTP connection handler, which breaks Tomcat6 when OpenDJ is an embeddedDS

* avoid initializing classes during class property value validation as this causes dependencies to be loaded which may be missing in the case where the component is disabled. The class will be fully loaded later if the component is enabled (verified with HTTP connection handler)
* prevent class loading errors from causing the server initialization to hang
* attempt to catch and propagate class loading errors up the stack. They are still not displayed in any logs (OPENDJ-1227).