Test for 'Origin by default', plus supporting tests & flags


* Add an '-insecureTLS' option, to disable cert checking
* Add a test to poll the CDN until it has successfully probed Origin 
* Add test code to check that a request will go to origin 'by default' (as in, not in the cache)

I think this could be reduced to:
```go
tlsOptions := &tls.Config{}
if *insecureTLS {
  tlsOptions.InsecureSkipVerify = true
}
```