Fix state.highstate run when using salt master

retcode-passthrough option is available only for masterless salt-call.
fix typos
Check whether Salt bootstrap script exists before attempting to delete it. GH-4614
Force compatible Bundler version in Travis
Merge pull request #4625 from tmatilai/travis_bundler

Force compatible Bundler version in Travis
docs - http sharing: fix typo
Merge pull request #4632 from janek-warchol/patch-1

docs - http sharing: fix typo
Allow SSH LogLevel to be overridden
Do not require rb-notify (temporary until we can upgrade middleman)
Update to the latest bundle to fix rubyracer issues
Add a note that VirtualBox supports parallelization
Add a note that VMWare does not support parallelization at this time
Add a note to check the docs
VirtualBox does not support it either
Merge pull request #4638 from julienvey/ssh_log_level

Allow SSH LogLevel to be overridden in Vagrant.Util.SSH.exec
whitespace
Merge pull request #4615 from styro/fix/master/issue-4614

provisoiners/salt: Check whether Salt bootstrap script exists before deleting it. GH-4614
Update CHANGELOG
Update wording for unreleased boxes
Merge pull request #4653 from mitchellh/sethvargo/document_parallel

website: vmware does not support --parallel