Prior to this commit, the puppet provisioner would not properly set its
environment variables, if any were configured in the Vagrantfile. This
commit separates those properly with semicolons when calling out to
puppet apply.
This commit sets the structured_facts option to nil if its still
UNSET_VALUE at the finalize step. This was causing a bug when the facter
config was set but was not using structured facts.
Prior to this commit, the puppet provisioner would use the manifest dir
flag when running `puppet apply`. Not only is this flag redundant due to
how puppet apply works, but it is also deprecated in Puppet 4 and
removed in Puppet 5. This commit simply removes the flag when invoking
`puppet apply`.
