How to get a list of existing variables from custom action plugin?

Hello everybody.

I am trying to update include_vars_merged (https://gist.github.com/udondan/b730206056a018cf9838) custom plugin to support ansible 2.0
I can’t find a right way to get a dict of already defined or loaded variables from custom action plugin - can somebody helps me?

Or maybe there are another way to get variables merged using include_vars action?

Alexey