Check whether Salt bootstrap script exists before attempting to delete it. GH-4614
Allow SSH LogLevel to be overridden
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