Unclosed aiohttp client session on clear action

[johhnry]

When sending a clear event on the /dcc/action route (you can kill the action from the interface), it stops the running action but the session is not closed:

$ rez env silex_client-dev -- silex action tester -c dev
Unclosed client session
client_session: <aiohttp.client.ClientSession object at 0x7feb2a515250>