We currently don't have test cases for _append, _prepend and _remove. This
patch adds some basic tests and includes a test case for a recently reported
issue with the _remove operator.
(Bitbake rev: 93291bd90e18808c7a1c8c692949396bbc7e4348)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>