Define ShouldRun for GcpTaskRunner and add --force for setup.

Skip the GCP setup task if the config already has fields set. And add
--force for setup args if user wants to re-initialize their config with
new values.

The checked fields are just for remote CF use right now.

Bug: 112615679
Test: acloud setup --gcp_init with config that has required fields defined
acloud setup --gcp_init --force still goes through setup steps.
atest acloud_test
Change-Id: I3fc27d556d828423da253237d570070f25f94bb9
diff --git a/setup/setup.py b/setup/setup.py
index ca34487..f7cf18e 100644
--- a/setup/setup.py
+++ b/setup/setup.py
@@ -53,7 +53,7 @@
         task_queue.append(gcp_runner)
 
     for subtask in task_queue:
-        subtask.Run()
+        subtask.Run(force_setup=args.force)
 
     # 3.Print the usage hints.
     _PrintUsage()