tests: extend ima tests for signature validation and exclude lists
tests: extend ima tests for signature validation and exclude lists

In c509dfb some behavior changes that were introduced during the move to
the IMA AST were fixed.
This extends the tests to cover more parts of the signature validation and
also adds checks for the exclude lists.

Signed-off-by: Thore Sommer <1d6e1cf70ec6f9ab28d3ea4b27a49a77654d370e@thson.de>

mit-ll/python-keylime,mit-ll/python-keylime,mit-ll/python-keylime,mit-ll/python-keylime