Introduce CELLSV2_SETUP variable

Some environments, like grenade and ironic, need a way to revert to
the non fleet version of the conductor setup. This really comes down
to a global topology for CELLSV2_SETUP. The prefered is with a
superconductor, but allow a downgrade to singleconductor.

Depends-On: I5390ec14c41da0237c898852935aba3569e7acae

Change-Id: I10fb048ef2175909019461e585d117b4284448c6
diff --git a/stackrc b/stackrc
index e526b54..877da82 100644
--- a/stackrc
+++ b/stackrc
@@ -77,6 +77,14 @@
 # Set the default Nova APIs to enable
 NOVA_ENABLED_APIS=osapi_compute,metadata
 
+# CELLSV2_SETUP - how we should configure services with cells v2
+#
+# - superconductor - this is one conductor for the api services, and
+#   one per cell managing the compute services. This is prefered
+# - singleconductor - this is one conductor for the whole deployment,
+#   this is not recommended, and will be removed in the future.
+CELLSV2_SETUP=${CELLSV2_SETUP:-"superconductor"}
+
 # Set the root URL for Horizon
 HORIZON_APACHE_ROOT="/dashboard"