Refactor network client: add create_ and update_ methods

Automatic create_ and update_ methods are added.
create_pool and update_pool modified in this patch serve
as an example of the usage.
For XML client simplistic json to xml serialization is used for now.

Change-Id: I8eb17d2aacfd4d2eacd8821b4b66e112626843a7
Merge "Refactor network client: add create_ and update_ methods"