Redstack guest agent fails if user not ubuntu

Added a chown command after useradd to change the ownership
to ${GUEST_USERNAME}
Also noted that the group being applied to GUEST_USERNAME
was incorrect - should be 'sudo'

Closes_Bug: #1317540

Change-Id: Ia670d8b8c9e7f9378a98c9fbc7885e187ef1aaa0