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
diff --git a/src/com/mirantis/mk/Openstack.groovy b/src/com/mirantis/mk/Openstack.groovy
index 8236ff3..fdaf014 100644
--- a/src/com/mirantis/mk/Openstack.groovy
+++ b/src/com/mirantis/mk/Openstack.groovy
@@ -264,10 +264,10 @@
  * @param path         Optional path to the custom virtualenv
  */
 def getHeatStackOutputParam(env, name, outputParam, path = null) {
-    cmd = "heat output-show ${name} ${outputParam}"
+    cmd = "openstack stack output show ${name} ${outputParam} -f value -c output_value"
     output = runOpenstackCommand(cmd, env, path)
     echo("${cmd}: ${output}")
-    return "${output}".substring(1, output.length()-1)
+    return "${output}"
 }
 
 /**