Python3:Replace iter.next() with next(iter)

function next() of iterator is not available in python3.
ref:http://www.diveintopython3.net/porting-code-to-python-3-with-2to3.html

Targets blueprint: murano-python-3-support

Change-Id: I8cb74520187ba532ad98b86b6ac15737a6cc9bee

contrib/plugins/murano_exampleplugin/murano_exampleplugin/__init__.py

@@ -38,7 +38,7 @@ class GlanceClient(object):
         images = self.client.images.list()
         while True:
             try:
-                image = images.next()
+                image = next(images)
                 yield GlanceClient._format(image)
             except StopIteration:
                 break

murano/engine/system/yaql_functions.py

@@ -179,7 +179,7 @@ def random_name():
 @specs.extension_method
 def first_or_default(collection, default=None):
     try:
-        return iter(collection).next()
+        return next(iter(collection))
     except StopIteration:
         return default