Force correct setup and cleanup for create_actors

[ceyhunsen]

Proposal Description

With the #570, create_actors won't spawn a Bitcoind client and don't accepts any parameter related to that. But that function needs a working Bitcoind client in order to function because it will create rpc clients inside. To prevent future problems, Bitcoind aliveness must be forced in compile time or checked in runtime to throw an error instead of confusing programmer.

Also, create_actor's last return parameter must live till' the end of the test. Is there anything we can do to force this behavior?