(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>