Don't output Concourse password to STDERR
Don't output Concourse password to STDERR

Stop the Concourse password from being written to STDERR each time something
calls `environment.sh`. This mostly happens on a developer's command line
when uploading pipelines, but also gets written into the task output of
Concourse tasks which call back to Concourse (e.g. self updating pipelines
and bosh-cli tests). Concourse has access to the whole environment so we
should be more protective of its password.

You'll still be able to get the password by running `make <env> showenv` and
it will still be output when running `make <env> bootstrap` which happens
less frequently and doesn't get called by Concourse itself.

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