NEXUS-5602: WL init add significant startup time.

This change now splits "WL init at boot" from "WL init
at repo addition on runtime" cases. Before, both were
doing same, but due to "cascade", one Nexus with lot of
repo and/or groups booted slower than before.

Now the "cascade" is not done in case of "boot" but on
"repo add at runtime" case is still done (and is needed).
On boot, extra step is done to explicitly init group reposes
WL, instead relying on having them updated implicitly due to
cascade.

This also meant, while former solution was correct, it was
sloppy as same group was updated over and over again on boot
process.

nexus-core/src/main/java/org/sonatype/nexus/proxy/maven/wl/internal/WLManagerImpl.java

@@ -181,11 +181,12 @@ public void startup()
             final ArrayList<MavenRepository> initableRepositories = new ArrayList<MavenRepository>();
             initableRepositories.addAll( repositoryRegistry.getRepositoriesWithFacet( MavenHostedRepository.class ) );
             initableRepositories.addAll( repositoryRegistry.getRepositoriesWithFacet( MavenProxyRepository.class ) );
+            initableRepositories.addAll( repositoryRegistry.getRepositoriesWithFacet( MavenGroupRepository.class ) );
             for ( MavenRepository mavenRepository : initableRepositories )
             {
                 if ( mavenRepository.getLocalStatus().shouldServiceRequest() )
                 {
-                    initializeWhitelist( mavenRepository );
+                    doInitializeWhitelist( mavenRepository, false );
                 }
             }
         }
@@ -225,10 +226,10 @@ public void shutdown()
     @Override
     public void initializeWhitelist( final MavenRepository mavenRepository )
     {
-        doInitializeWhitelist( mavenRepository );
+        doInitializeWhitelist( mavenRepository, true );
     }
 
-    protected void doInitializeWhitelist( final MavenRepository mavenRepository )
+    protected void doInitializeWhitelist( final MavenRepository mavenRepository, final boolean propagate )
     {
         getLogger().debug( "Initializing white-list of {}",
             RepositoryStringUtils.getHumanizedNameString( mavenRepository ) );
@@ -239,15 +240,15 @@ protected void doInitializeWhitelist( final MavenRepository mavenRepository )
             {
                 // good, we assume is up to date, which should be unless user tampered with it
                 // in that case, just delete it + update and should be fixed.
-                publish( mavenRepository, prefixSource );
+                publish( mavenRepository, prefixSource, propagate );
                 getLogger().info( "Existing white-list of {} initialized",
                     RepositoryStringUtils.getHumanizedNameString( mavenRepository ) );
             }
             else
             {
                 // mark it for noscrape if not marked yet
                 // this is mainly important on 1st boot or newly added reposes
-                unpublish( mavenRepository );
+                unpublish( mavenRepository, propagate );
                 // spawn update, this will do whatever is needed (and handle cases like blocked, out of service etc),
                 // publish
                 updateWhitelist( mavenRepository );
@@ -261,7 +262,7 @@ protected void doInitializeWhitelist( final MavenRepository mavenRepository )
                 RepositoryStringUtils.getHumanizedNameString( mavenRepository ), e );
             try
             {
-                unpublish( mavenRepository );
+                unpublish( mavenRepository, propagate );
             }
             catch ( IOException ioe )
             {
@@ -979,6 +980,13 @@ public boolean revokeWLEntry( final MavenHostedRepository mavenHostedRepository,
     @Override
     public void publish( final MavenRepository mavenRepository, final PrefixSource prefixSource )
         throws IOException
+    {
+        publish( mavenRepository, prefixSource, true );
+    }
+
+    protected void publish( final MavenRepository mavenRepository, final PrefixSource prefixSource,
+                            final boolean propagate )
+        throws IOException
     {
         // publish prefix file
         final FilePrefixSource prefixesFile = getPrefixSourceFor( mavenRepository );
@@ -998,13 +1006,22 @@ public void publish( final MavenRepository mavenRepository, final PrefixSource p
         // event
         eventBus.post( new WLPublishedRepositoryEvent( mavenRepository, prefixesFile ) );
 
-        // propagate
-        propagateWLUpdateOf( mavenRepository );
+        if ( propagate )
+        {
+            // propagate
+            propagateWLUpdateOf( mavenRepository );
+        }
     }
 
     @Override
     public void unpublish( final MavenRepository mavenRepository )
         throws IOException
+    {
+        unpublish( mavenRepository, true );
+    }
+
+    protected void unpublish( final MavenRepository mavenRepository, final boolean propagate )
+        throws IOException
     {
         // delete (if any) published files, even those that user might manually put there
         getPrefixSourceFor( mavenRepository ).delete();
@@ -1022,8 +1039,11 @@ public void unpublish( final MavenRepository mavenRepository )
         // event
         eventBus.post( new WLUnpublishedRepositoryEvent( mavenRepository ) );
 
-        // propagate
-        propagateWLUpdateOf( mavenRepository );
+        if ( propagate )
+        {
+            // propagate
+            propagateWLUpdateOf( mavenRepository );
+        }
     }
 
     protected void propagateWLUpdateOf( final MavenRepository mavenRepository )