Add system test which randomly selects $DEFAULT_ALGORITHM
DEFAULT_ALGORITHM for testing to
ECDSAP256SHA256 (other variables like
DEFAULT_HMAC, etc. follow from this). We should have a daily CI job which randomly - on runtime - sets
DEFAULT_ALGORITHM et al. from algorithms allowed on the current system to ensure that system test continues to work for all supported algorithms where possible.
(Requested by @marka on Friday.)