Add wait for app to be routable function in library.sh (knative#128)

* Add wait for app to be routable function in library

* Add function documentation

* Make log statements better

* Nuke stderr

* Assorted nits

* indentation, punctuation, linefeeds
* add log message about what the function is doing 
* use the same loop pattern as the other functions

scripts/library.sh

@@ -154,6 +154,24 @@ function wait_until_service_has_external_ip() {
   return 1
 }
 
+# Waits for the endpoint to be routable.
+# Parameters: $1 - External ingress IP address.
+#             $2 - cluster hostname.
+function wait_until_routable() {
+  echo -n "Waiting until cluster $2 at $1 has a routable endpoint"
+  for i in {1..150}; do  # timeout after 5 minutes
+    local val=$(curl -H "Host: $2" "http://$1" 2>/dev/null)
+    if [[ -n "$val" ]]; then
+      echo "\nEndpoint is now routable"
+      return 0
+    fi
+    echo -n "."
+    sleep 2
+  done
+  echo -e "\n\nERROR: Timed out waiting for endpoint to be routable"
+  return 1
+}
+
 # Returns the name of the pod of the given app.
 # Parameters: $1 - app name.
 #             $2 - namespace (optional).