Merge pull request #3987 from jglick/slave-installer

[JENKINS-57071] Fixing problems affecting Linux agent installer modules

core/src/main/java/hudson/os/SU.java

@@ -155,7 +155,7 @@ public abstract class SU {
             else // in production code this never happens, but during debugging this is convenient    
                 args.add("-cp").add(slaveJar).add(hudson.remoting.Launcher.class.getName());
 
-            if(rootPassword==null) {
+            if (Util.fixEmptyAndTrim(rootPassword) == null) {
                 // try sudo, in the hope that the user has the permission to do so without password
                 return new LocalLauncher(listener).launchChannel(
                         args.prepend(sudoExe()).toCommandArray(),

core/src/main/java/jenkins/security/ChannelConfigurator.java

@@ -5,7 +5,6 @@ import hudson.ExtensionPoint;
 import hudson.remoting.Channel;
 import hudson.remoting.ChannelBuilder;
 import hudson.slaves.SlaveComputer;
-import jenkins.model.Jenkins;
 
 import javax.annotation.Nullable;
 
@@ -39,6 +38,6 @@ public abstract class ChannelConfigurator implements ExtensionPoint {
      * All the registered {@link ChannelConfigurator}s.
      */
     public static ExtensionList<ChannelConfigurator> all() {
-        return Jenkins.getInstance().getExtensionList(ChannelConfigurator.class);
+        return ExtensionList.lookup(ChannelConfigurator.class);
     }
 }