Declare test to throw multiple exception types

Common practice that any exception thrown in the test will fail the
tes

src/test/java/com/nirima/jenkins/plugins/docker/DockerCloudTest.java

@@ -187,7 +187,7 @@ private static void assertCount(
     }
 
     @Test
-    public void testRegistryCredentials() throws IOException {
+    public void testRegistryCredentials() throws Exception {
 
         final CredentialsStore store = CredentialsProvider.lookupStores(jenkins.getInstance())
                 .iterator()