The task was originally separating NON_PRODUCTION_FILES.txt out of the
bin_gpdb tarball and putting them into the QAUTILS_TARBALL, and leaving
OUTPUT_TARBALL with the rest of the files.
However, QAUTILS_TARBALL is never used, the only important function is
to remove the NON_PRODUCTION_FILES.txt.

With this commit, we refactor the separate_qautils_files to only remove
files. Also, we introduce a new pattern for TDD'ing bash scripts by
using the MIT-licensed BATS framework.
Co-authored-by: NMark Sliva <msliva@pivotal.io>
Co-authored-by: NAmil Khanzada <akhanzada@pivotal.io>
(cherry-picked from 5458b94b)