Force overwrite of salt configs and keys.

This will tell the salt-bootstrap script to overwrite the master/minion
configs and/or keys each time provision is called. #3524 #3176
Merge pull request #3536 from shadowfax-chc/force-overwrite-salt-configs

provisioners/salt: force overwrite of salt configs and keys.
Update CHANGELOG
website/www: add latest-version.json to website
commands/version: check latest version
core: add Vagrant.latest_version
Merge pull request #3540 from mitchellh/f-version-command

vagrant version command
Update CHANGELOG
Revert "core: can't add boxes from network shares [GH-3279]"

This reverts commit 41636a8a9cefa68d18e641efee9fc410ed1dd1d4.

Conflicts:
	CHANGELOG.md
Update CHANGELOG
core: more liberally release port leases
core: delete environment lock files
core: clean up the lock cleanup code, tests
core: Box#in_use? as an API
provisioners/ansible: minor change in unit tests

Combine a maximum of options in the last test:
- Ansible Vault options from [GH-3338]
- raw_arguments

Note: it is not expected from Vagrant to reject incoherent combinations
provisioners/ansible: fix an error in a unit test
provisioners/ansible: Don't run with two --limits

Conflicts:
	test/unit/plugins/provisioners/ansible/provisioner_test.rb
provisioners/ansible: fix unit tests for [GH-3491]
synced_folders/rsync: only chown when necessary [GH-3525]

Run remote rsync as root to guarantee that rsync can write to guestpath.
This obviates the need to chown the guestpath to the SSH user prior to
sync.

This brings a substantial speedup (2x on a moderately-sized shared
folder) and properly triggers filesystem notifications on only the files
changed by a given sync.
core: return {} if cached synced folders file missing [GH-3550]

A missing synced folders cache indicates an empty cache, not a failure
that should be handled by the caller. The cache file is missing from
data dirs created by an earlier version of Vagrant.

Fixes #3550.