Default Q_HOST to HOST_IP rather than localhost.

This makes it less likely to interact with e.g. http_proxy settings.

I filed this as bug 1080561.

Change-Id: If97459a28f2d2a77cd322bb3f6024d11fbb8fcd4
diff --git a/stack.sh b/stack.sh
index ec10b11..70c9e04 100755
--- a/stack.sh
+++ b/stack.sh
@@ -330,7 +330,7 @@
 # Default Quantum Port
 Q_PORT=${Q_PORT:-9696}
 # Default Quantum Host
-Q_HOST=${Q_HOST:-localhost}
+Q_HOST=${Q_HOST:-$HOST_IP}
 # Which Quantum API nova should use
 # Default admin username
 Q_ADMIN_USERNAME=${Q_ADMIN_USERNAME:-quantum}