Integrate create_tenant with the initial_setup command

[atodorov]

Upstream Kiwi TCMS has a nice single-entry setup command called initial_setup which executes other setup commands as necessary. However this mechanism doesn't include the create_tenant command nor does it provide machinery to automatically execute commands from add-on plugins.

There's a secondary dependency in this case - the domain name for the first tenant is also the domain name provided in set_domain.

CC @schwarzkrieger