Make output_env struct properly private/opaque.

Make output_env struct properly private/opaque.

All the necessary functions already existed to make the structure
private, only the signature of the initialization functions needed to be
changed.  Adjusted places where the structure was initialized to not
access the internals of the structure, but do everything through the
initialization functions.

Change-Id: Ia1f7fdeccd0678e41b5af4256fcf6f7a4014c59d