Make tests pass with buildFunc
Make tests pass with buildFunc

Commit 45c858b5451e949d4d62642de48bb15a9d38be14 has a test that mocks the builder object. That was removed on the v2 branch. This PR adjusts the tests to pass using the buildFunc instead.

Signed-off-by: Daniel Mikusa <f34d11341ccdc5b8ff9432e6eb24655a0645e514@vmware.com>

buildpacks/libcnb