Running the entropy unit test creates a suitable seedfile, but this
only works due to the happy accident that no prior unit test needs one
(specifically, test_suite_entropy runs before test_suite_rsa). So
create one explicitly, both for robustness and to keep the script
closer to the version in development where the explicit seedfile
creation is required.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>