Make image_list.sh independent of host IP address

We do not need the HOST_IP to be detected in order to be able to list
our images. So just set that to some dummy value before sourcing
functions.

This will allow tools like disk-image-builder to work regardless of
whether get_default_host_ip succeeds or not.

Change-Id: I9c22d2066e34309e70e56076e3d17c5db6ecee06
diff --git a/tools/image_list.sh b/tools/image_list.sh
index a27635e..27b3d46 100755
--- a/tools/image_list.sh
+++ b/tools/image_list.sh
@@ -3,6 +3,12 @@
 # Keep track of the DevStack directory
 TOP_DIR=$(cd $(dirname "$0")/.. && pwd)
 
+# The following "source" implicitly calls get_default_host_ip() in
+# stackrc and will die if the selected default IP happens to lie
+# in the default ranges for FIXED_RANGE or FLOATING_RANGE. Since we
+# do not really need HOST_IP to be properly set in the remainder of
+# this script, just set it to some dummy value and make stackrc happy.
+HOST_IP=SKIP
 source $TOP_DIR/functions
 
 # Possible virt drivers, if we have more, add them here. Always keep