Disable rax-ord and rax-iad

These regions do not appear to be functioning normally (with
servers unable to be deleted), remove them from service.

Change-Id: Iddb7a218a305cc0f73e3bf702f91e47c8729de98

zuul.d/providers.yaml

@@ -100,6 +100,8 @@
     name: rax-iad
     parent: rax-base
     region: IAD
+    resource-limits:
+      instances: 0
 
 - provider:
     name: rax-iad-main
@@ -117,6 +119,8 @@
     # launch in parallel.
     # Not implemented in NIZ:
     # max-concurrency: 5
+    resource-limits:
+      instances: 0
 
 - provider:
     name: rax-ord-main