various context related cleanups to rest.Request

* Move all usage of r.ctx to the beginning of Do, DoRaw, Stream, Watch
* Move tryThrottle from Do and DoRaw into request()
* Make request() and tryThrottle take a context
* In request(), remove the timeout context setting out of the loop

These changes should be entirely behavior preserving.

staging/src/k8s.io/client-go/rest/request.go

@@ -786,6 +786,7 @@ func (r *Request) request(ctx context.Context, fn func(*http.Request, *http.Resp
 	maxRetries := 10
 	retries := 0
 	for {
+
 		url := r.URL().String()
 		req, err := http.NewRequest(r.verb, url, r.body)
 		if err != nil {