Fix getting stack ip for heatclient > 1.5.1

heatclient with verstion <=1.5.1 returns value in '""' when calling
'heat output-show' while newer versions returns value without '""'
Use 'openstack stack output show' instead which produce the same output
for all heatclient versions.

Change-Id: I15677826d89b7db28268bf075e644ae20785836b
1 file changed