exercises: Multihost support for Glance client

floating_ips and volumes exercises both access Glance directly, but
assume it is running locally.  To better accomodate exercising a
multi-host cloud, specify glance host via GLANCE_HOST setting which
defaults to HOST_IP to maintain current single-node functionality.

Change-Id: Iad06044af031083afa477204d446ada5161ca521
diff --git a/exercises/volumes.sh b/exercises/volumes.sh
index c2288de..3f75483 100755
--- a/exercises/volumes.sh
+++ b/exercises/volumes.sh
@@ -56,10 +56,10 @@
 nova image-list
 
 # But we recommend using glance directly
-glance -f -A $TOKEN index
+glance -f -A $TOKEN -H $GLANCE_HOST index
 
 # Grab the id of the image to launch
-IMAGE=`glance -f -A $TOKEN index | egrep $DEFAULT_IMAGE_NAME | head -1 | cut -d" " -f1`
+IMAGE=`glance -f -A $TOKEN -H $GLANCE_HOST index | egrep $DEFAULT_IMAGE_NAME | head -1 | cut -d" " -f1`
 
 # determinine instance type
 # -------------------------