Rename docker_client and docker_installer

We can rename those classes and remove the docker_ prefix as they
already have a module namespace.
website/docs: phrasal verbs [GH-2644]
core: box removal of a V1 box works
Merge pull request #2641 from arthurnn/docker_rename

Rename docker_client and docker_installer
Update CHANGELOG
provisioners/chef: fix node/client deletion when node_name is not set [GH-2345]

V2 config uses `hostname` instead of `host_name`.