fix serializable errors

previous code fails with java.io.NotSerializableException

Change-Id: I47866d320612fdf6dd1223d75a9cc7e452fbec44
diff --git a/src/com/mirantis/mk/Openstack.groovy b/src/com/mirantis/mk/Openstack.groovy
index 664e558..1d79ea3 100644
--- a/src/com/mirantis/mk/Openstack.groovy
+++ b/src/com/mirantis/mk/Openstack.groovy
@@ -121,8 +121,9 @@
         envString = "parameters:\n"
     }
 
-    for (item in environment) {
-        envString = "${envString}  ${item.key}: ${item.value}\n"
+    def p = environment.collect {k, v -> [k, v]}
+    for (int i = 0; i < p.size(); i++) {
+        envString = "${envString}  ${p.get(i)[0]}: ${p.get(i)[1]}\n"
     }
 
     echo("writing to env file:\n${envString}")