Unnamed Docker volumes for stclient

[dr-yd]

Describe the problem
st2client uses the st2actionrunner image which has volumes defined for ["/home/stanley/.ssh", "/opt/stackstorm/packs", "/opt/stackstorm/virtualenvs"] and is derived from st2 which has ["/etc/st2"]. These volumes are created as empty for the st2client which is confusing, in this case for our volume-level backup as the generated IDs are obfuscating where these volumes are coming from. If the client needs its own volumes in their place, they should be created and the association with the client container be made clear; if it doesn't matter because the contents aren't used, the simplest solution would be to still mount the volumes which the other containers are using in the same place.

Versions
[not relevant]

To Reproduce
Deploy the docker-compose.yml.