bitbake: test/data: Add new tests for task checksum changing/not changing

bitbake: test/data: Add new tests for task checksum changing/not changing

This adds some basic tests for task checksums to ensure that the
checksums:

* change when variables change
* change when active _remove operators are present
* don't change when the _remove operators are not active
* change when an active contains() expression is present
* dont' change a contains() expression isn't active

There is a lot of other functionality which should be added to this
test but its a start.

(Bitbake rev: 5463c16e3619d324aed137f47f93f0997a227d29)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>