providers/docker: be more lenient about deleting built image
providers/docker: expand path to share relative to docker env
synced_folders/rsync: fix oddness on Windows
commands/init: force flag [GH-3564]
[ci skip] Fix a typo in bin/vagrant comment.
Merge pull request #3572 from JuanitoFatas/patch/fix-a-typo

[ci skip] Fix a typo in bin/vagrant comment.
Set u+w perms on private keys in tmp dir.

This should allow additional `vagrant provision` calls to work when
using the salt provisioner and providing private keys. See #3542.
Merge pull request #3575 from shadowfax-chc/salt-provision-private-key-perms

provisioner/salt: Set u+w perms on private keys in tmp dir.
Update CHANGELOG.md
website/www: feature preview docker provider
providers/docker: raise better error for local executor
providers/docker: clearer options on docker-logs
providers/docker: pty flag, not functional yet
add dependency on Ruby >= 2.0.0

Vagrant requires Ruby 2, e.g. for ** keyword arguments.
providers/docker: use ssh_run if asking for stdin on execute
providers/docker: with a pty, single target the docker-run cmd
Merge pull request #3580 from mitchellh/f-tty-docker-run

vagrant docker-run tty
Removing some old files
Handle a lot of TODOs
core: Lock in plugin install of a specific version