Restructure platform test setup

Current setup sucks for various reasons:

• testing hosts are tied to vagrant
• leap_cli, provider config and hosts need to be on one machine
• greyhound is at its mem limits

Much better would be:

• integrate fog into leap_cli so we can start/stop/destroy remote hosts from leap_cli
• ability to import provider config from single (json) file

(from redmine: created on 2016-01-27, closed on 2016-11-08, relates #7845)