unset basic auth creds when they are not passed
unset basic auth creds when they are not passed

[#109493662]

Signed-off-by: Liz Dahlstrom <3d0432bc57a726c6c6e52e5386d47f2dc42064ee@pivotal.io>

concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse