cmd/browser: sleep between checking on service management operations

When enabling a Cloud API using the Service Management API you first
make the enable request and then make a series of requests to check on
the status of that enable operation. To avoid running over the Service
Management API Quota, we should sleep a bit between checks.

Fix upspin/upspin#466

Change-Id: Ica2fb8b0294e2fef9c6d814907ce9eac6f69d137
Reviewed-on: https://upspin-review.googlesource.com/13500
Reviewed-by: Rob Pike <r@golang.org>
diff --git a/cmd/browser/gcp.go b/cmd/browser/gcp.go
index 8a1796e..3a0bbe9 100644
--- a/cmd/browser/gcp.go
+++ b/cmd/browser/gcp.go
@@ -179,6 +179,7 @@
 		return err
 	}
 	for !op.Done {
+		time.Sleep(250 * time.Millisecond)
 		op, err = svc.Operations.Get(op.Name).Do()
 		if err != nil {
 			return err