Increase backoff period from 100 to 500

This increases the overall test execution time but makes it less likely
to fail on slow test machines.

core/src/test/java/org/jclouds/http/handlers/BackoffLimitedRetryHandlerTest.java

@@ -61,7 +61,7 @@ public class BackoffLimitedRetryHandlerTest {
 
    @Test
    void testExponentialBackoffDelayDefaultMaxInterval500() throws InterruptedException {
-      long period = 100;
+      long period = 500;
       long acceptableDelay = period - 1;
 
       long startTime = System.nanoTime();