Allow packstack to detect linux sub-interfaces properly

Change-Id: Iebc764c1bf9fa6639cb81f0aa9d45eab4c176424

packstack/installer/utils/network.py

@@ -76,8 +76,10 @@ def force_ip(host, allow_localhost=False):
 
 def device_from_ip(ip):
     server = ScriptRunner()
-    server.append("DEVICE=$(ip address show to %s | head -n 1 |"
-                  " sed -e 's/.*: \(.*\):.*/\\1/g')" % ip)
+    server.append("DEVICE=($(ip -o address show to %s | cut -f 2 -d ' '))"
+                  % ip)
+    # Ensure that the IP is only assigned to one interface
+    server.append("if [ ! -z ${DISPLAY[1]} ]; then false; fi")
     # Test device, raises an exception if it doesn't exist
     server.append("ip link show \"$DEVICE\" > /dev/null")
     server.append("echo $DEVICE")