Move all test cases from tests.sh to tests_ksr.py. The only test that
is not moved is the check that key id's match expected keys. The
shell-based system test checks two earlier set environment variables
against each other that has become redundant in the pytest variant,
because we now check the signed key response against a list of keys
and for each key we take into account the timing metadata. So we
already ensure that each published key is in the correct key bundle.
(cherry picked from commit a15bf6704b)
288dce213a