PR #14771 added support for getting certs from alternate ACME servers, but the
certStore caching mechanism breaks unless you install the CA in system roots,
because we check the validity of the cert before allowing a cache hit, which
includes checking for a valid chain back to a trusted CA. For ease of testing,
allow cert cache hits when the chain is unknown to avoid re-issuing the cert
on every TLS request served. We will still get a cache miss when the cert has
expired, as enforced by a test, and this makes it much easier to test against
non-prod ACME servers compared to having to manage the installation of non-prod
CAs on clients.
Updates #14771
Change-Id: I74fe6593fe399bd135cc822195155e99985ec08a
Signed-off-by: Tom Proctor <tomhjp@users.noreply.github.com>