Do not initialize the Fake backend on the start

The Fake backend requires a new format of configuration. An example of
the format is:

        fake:
            delays: true
            num_hypervisors: 8
            populate:
                num_tenants: 20
                num_servers: 15

where

* num_hypervisors – a number of hosts in the cloud
* pupulate – is an optional, if present then the cloud would
    be populated by tenants and servers.
    * num_tenants – a number of tenants for population
    * num_servers – a number of servers for population