[JENKINS-18922] Trying to make this error (missing maven-plugin) nonfatal during startup.

May not suffice: a fatal error may simply be thrown later on.

core/src/main/java/hudson/model/UpdateCenter.java

@@ -1544,7 +1544,7 @@ public class UpdateCenter extends AbstractModelObject implements Saveable, OnMas
      *
      * This has to wait until after all plugins load, to let custom UpdateCenterConfiguration take effect first.
      */
-    @Initializer(after=PLUGINS_STARTED)
+    @Initializer(after=PLUGINS_STARTED, fatal=false)
     public static void init(Jenkins h) throws IOException {
         h.getUpdateCenter().load();
     }

core/src/main/java/hudson/model/listeners/SaveableListener.java

@@ -30,6 +30,8 @@ import hudson.ExtensionList;
 import hudson.XmlFile;
 import jenkins.model.Jenkins;
 import hudson.model.Saveable;
+import java.util.logging.Level;
+import java.util.logging.Logger;
 
 /**
  * Receives notifications about save actions on {@link Saveable} objects in Hudson.
@@ -75,7 +77,13 @@ public abstract class SaveableListener implements ExtensionPoint {
      */
     public static void fireOnChange(Saveable o, XmlFile file) {
         for (SaveableListener l : all()) {
-            l.onChange(o,file);
+            try {
+                l.onChange(o,file);
+            } catch (ThreadDeath t) {
+                throw t;
+            } catch (Throwable t) {
+                Logger.getLogger(SaveableListener.class.getName()).log(Level.WARNING, null, t);
+            }
         }
     }