(PE-4848,PUP-2999) Ensure temporary directories ownership is correct.

`master['user']` has a default value of `root` specified in Beaker::Host::Unix.
As it turns out, this is the config option containing the username used to log
in to SUTs.

It's better then to use `on master, 'puppet master --configprint user'` since
this will always give us the actual puppet user, whether it's `puppet` or
`pe-puppet` or something else.

Also, it's best to use the `create_tmpdir_for_user` method when initially
creating temporary directories on SUTs since `host.tmpdir` will always create
directories owned by root.

Signed-off-by: Wayne <wayne@puppetlabs.com>