Allocate new container name using prefix

Before we used the previous container name, which kept appending and
hit S3 limits during integration tests like:

Caused by: java.lang.IllegalArgumentException: Object 'gaul-blobstore27-4348532805015069992-1155797412711190448-1465016400636204031' doesn't match S3 bucket virtual host naming convention. Reason: Can't be null or empty. Length must be 3 to 63 symbols.. For more info, please refer to http://docs.amazonwebservices.com/AmazonS3/latest/index.html?BucketRestrictions.html

blobstore/src/test/java/org/jclouds/blobstore/integration/internal/BaseBlobStoreIntegrationTest.java

@@ -499,7 +499,7 @@ public class BaseBlobStoreIntegrationTest extends BaseViewLiveTest<BlobStoreCont
             deleteContainerOrWarnIfUnable(view, container);
          }
       });
-      String newScratchContainer = container + new SecureRandom().nextLong();
+      String newScratchContainer = CONTAINER_PREFIX + new SecureRandom().nextLong();
       System.err.printf("*** allocated new container %s...%n", container);
       return newScratchContainer;
    }