HOTFIX: disable pushing stats to Coveralls

Seems to be broken atm.
Refactor: pass sandbox path and root path to provisioner

And remove common functions shared by all provisioners.
Refactor: rename CreateSandbox to PrepareFiles

And get rid of CleanupSandbox, which wasn't used anyway.
Refactor: decouple provisioning from resolving cookbooks
Refactor: decouple provisioning from installing Chef
Refactor: restore original order of actions
Refactor: create sandbox outside of provisioner
Refactor: consistent naming/logging