[FIXED JENKINS-33414] Added an API to allow identification of the Jenkins JVM

- Fix the ProxyConfiguration code to not require Jenkins class to be loaded in remote JVMs

core/src/test/java/jenkins/util/JenkinsJVMTest.java

@@ -0,0 +1,36 @@
+package jenkins.util;
+
+import org.junit.Test;
+
+public class JenkinsJVMTest {
+
+    @Test
+    public void checkNotJenkinsJVM_WhenNotInAJenkinsJVM() {
+        JenkinsJVM.checkNotJenkinsJVM();
+    }
+
+    @Test(expected = IllegalStateException.class)
+    public void checkJenkinsJVM_WhenNotInAJenkinsJVM() {
+        JenkinsJVM.checkJenkinsJVM();
+    }
+
+    @Test(expected = IllegalStateException.class)
+    public void checkNotJenkinsJVM_WhenInAJenkinsJVM() {
+        JenkinsJVM.setJenkinsJVM(true);
+        try {
+            JenkinsJVM.checkNotJenkinsJVM();
+        } finally {
+            JenkinsJVM.setJenkinsJVM(false);
+        }
+    }
+
+    @Test
+    public void checkJenkinsJVM_WhenInAJenkinsJVM() {
+        JenkinsJVM.setJenkinsJVM(true);
+        try {
+            JenkinsJVM.checkJenkinsJVM();
+        } finally {
+            JenkinsJVM.setJenkinsJVM(false);
+        }
+    }
+}