Skip a test if starting Jenkins was interrupted.

For reasons TBD, sometimes CI tests fail with (1.565.x):
java.lang.InterruptedException: null
	at java.lang.Object.wait(Native Method)
	at java.lang.Object.wait(Object.java:503)
	at org.jvnet.hudson.reactor.Reactor.execute(Reactor.java:267)
	at jenkins.InitReactorRunner.run(InitReactorRunner.java:44)
	at jenkins.model.Jenkins.executeReactor(Jenkins.java:915)
	at jenkins.model.Jenkins.<init>(Jenkins.java:814)
	at hudson.model.Hudson.<init>(Hudson.java:82)
	at org.jvnet.hudson.test.JenkinsRule.newHudson(JenkinsRule.java:539)
	at org.jvnet.hudson.test.JenkinsRule.before(JenkinsRule.java:331)
	at org.jvnet.hudson.test.JenkinsRule$2.evaluate(JenkinsRule.java:479)

test/src/main/java/org/jvnet/hudson/test/JenkinsRule.java

@@ -531,7 +531,11 @@ public class JenkinsRule implements TestRule, MethodRule, RootAction {
         File home = homeLoader.allocate();
         for (JenkinsRecipe.Runner r : recipes)
             r.decorateHome(this,home);
-        return new Hudson(home, webServer, getPluginManager());
+        try {
+            return new Hudson(home, webServer, getPluginManager());
+        } catch (InterruptedException x) {
+            throw new AssumptionViolatedException("Jenkins startup interrupted", x);
+        }
     }
 
     public PluginManager getPluginManager() {