MbedTLS sign certificate

[huitema]

No description provided.

[huitema]

@kazuho the red flag in the test results comes from an appveyor issue, when running the 32 bit "debug" test:

Build started
git clone -q https://github.com/h2o/picotls.git C:\projects\picotls
fatal: unable to access 'https://github.com/h2o/picotls.git/': Failed to connect to github.com port 443: Timed out
Command exited with code 128

I have seen that on a couple occasions with Picoquic. Just restarting the test would fix it, but I think I don't have the permission to do that in the picotls depot. In any case, the 32 bit "release" test works, as well as the 64 bit "debug" test, so we are very unlikely to find an issue.

[kazuho]

Thank you for the PR. Merged as #517.