fix findbugs warnings in ExponentialDelay, RandomDelay and RandomExpo…

…nentialDelay

src/main/java/org/jenkinsci/plugins/workflow/support/steps/retry/ExponentialDelay.java

@@ -19,10 +19,11 @@
 @Extension
 public class ExponentialDelay extends RetryDelay implements Serializable {
 
+    private static final int base = 2;
+
     private final long min;
     private final long max;
     private final int multiplier;
-    private final int base = 2;
     private int lastMultiplier = 0;
 
     public ExponentialDelay() { 

src/main/java/org/jenkinsci/plugins/workflow/support/steps/retry/RandomDelay.java

@@ -16,9 +16,10 @@
 @Extension
 public class RandomDelay extends RetryDelay implements Serializable {
 
+    private static final Random RANDOM = new Random();
+
     private final int min;
     private final int max;
-    private Random random = new Random();
 
     public RandomDelay() { 
         super();
@@ -42,11 +43,11 @@ public long getMax() {
 
     @Override
     public long computeRetryDelay() {
-        long delay = min;
+        long delay;
         if(min == max) {
             delay = min;
         } else {
-            delay = random.nextInt(max-min) + min;
+            delay = RANDOM.nextInt(max-min) + min;
         }
 
         return unit.toMillis(delay);

src/main/java/org/jenkinsci/plugins/workflow/support/steps/retry/RandomExponentialDelay.java

@@ -19,12 +19,13 @@
 @Extension
 public class RandomExponentialDelay extends RetryDelay implements Serializable {
 
+    private static final int base = 2;
+    private static final Random RANDOM = new Random();
+
     private final int multiplier;
     private final int max;
-    private final int base = 2;
     private boolean largerThanMax = false;
     private int lastMultiplier = 0;
-    private Random random = new Random();
 
     public RandomExponentialDelay() { 
         super();
@@ -48,9 +49,9 @@ public long getMax() {
 
     @Override
     public long computeRetryDelay() {
-        long delay = 0;
+        long delay;
         if(largerThanMax) {
-            delay = 1 + random.nextInt(max);
+            delay = 1 + RANDOM.nextInt(max);
         } else {
             if(lastMultiplier > 0) {
                 lastMultiplier += 1;