Connect to a running tor only for chutney tests

[juga0]

Since bwscan can launch tor and connecting to a running tor is only needed for chutney, it would be probably safer to allow connecting to tor only for chutney.

See comment in #85 (comment)

In the case we want to leave the possibility to connect to a running tor, it should not fail silently when the user running bwscan does not have privileges for cookie authentication (this should probably be in other ticket)