start asn1, public_key
    ct_slave: ssh_port, ssh_opts options to start/3

Using these new options it is possible to specify ssh_port in a .spec file:
[{node_start, [{ssh_port, 9999}]}].

And also to specify additional ssh options like paths to public-key files:
[{node_start, [{ssh_opts, [{user_dir, "/home/shrek/e2/"}]}]}].