Make Classworld setup more alike to vanilla Maven (#784)

Use the plexus Launcher to start the daemon server, just like we would
launch a normal Maven process.

This improves compatibility with any extensions or plugins that assume that
their ClassLoader is a ClassRealm.

dist/src/main/distro/bin/mvnd-server.conf

@@ -0,0 +1,25 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+main is org.mvndaemon.mvnd.daemon.Server from plexus.core
+
+set maven.home default ${mvnd.home}
+set maven.conf default ${maven.home}/conf
+
+[plexus.core]
+load       ${maven.conf}/logging
+optionally ${maven.home}/lib/ext/*.jar
+load       ${maven.home}/lib/*.jar