deploy: Add logging

so the user can better understand what's going on.

I found this useful to prove that my previous PR was working and to better understand what happens when a Python app is deployed via Tsuru.

It outputs logging like this:

```
...
remote: *** /var/lib/tsuru/deploy: ${SOURCE_DIR} = "/var/lib/tsuru"
...
remote: *** /var/lib/tsuru/deploy: About to do pip install (pwd: /home/application/current)
...
remote: *** /var/lib/tsuru/deploy: Running any hooks in /var/lib/tsuru/hooks.py (pwd: /)
remote: *** /var/lib/tsuru/deploy: Done.
...
```