fix "TypeError: Object of type map is not JSON serializable" (#223)

Fix TypeError for manageiq_provider module.

changelogs/fragments/223-manageiq_provider-fix-serialization.yml

@@ -0,0 +1,2 @@
+bugfixes:
+- manageiq_provider - fix serialization error when running on python3 environment.

plugins/modules/remote_management/manageiq/manageiq_provider.py

@@ -571,7 +571,7 @@ def delete_nulls(h):
         a hash without nulls
     """
     if isinstance(h, list):
-        return map(delete_nulls, h)
+        return [delete_nulls(i) for i in h]
     if isinstance(h, dict):
         return dict((k, delete_nulls(v)) for k, v in h.items() if v is not None)