[MRM-1864] use SSL by default for central

This matches the default configuration used in the latest version of Maven.

archiva-modules/archiva-base/archiva-configuration/src/main/resources/org/apache/archiva/configuration/default-archiva.xml

@@ -33,7 +33,7 @@
     <remoteRepository>
       <id>central</id>
       <name>Central Repository</name>
-      <url>http://repo.maven.apache.org/maven2</url>
+      <url>https://repo.maven.apache.org/maven2</url>
       <layout>default</layout>
     </remoteRepository>
   </remoteRepositories>

archiva-modules/archiva-base/archiva-repository-admin/archiva-repository-admin-default/src/test/java/org/apache/archiva/admin/repository/remote/RemoteRepositoryAdminTest.java

@@ -48,7 +48,7 @@ public class RemoteRepositoryAdminTest
     {
         RemoteRepository central = remoteRepositoryAdmin.getRemoteRepository( "central" );
         assertNotNull( central );
-        assertEquals( "http://repo.maven.apache.org/maven2", central.getUrl() );
+        assertEquals( "https://repo.maven.apache.org/maven2", central.getUrl() );
         assertEquals( 60, central.getTimeout() );
         assertNull( central.getUserName() );
         assertNull( central.getPassword() );