fix bad nonce

[christianhoelzl]

Any ACME CA that generate bad nonce responses often (e.g. Pebble CA 5% of all requests) can lead to unexpected errors in the public API ("urn:ietf:params:acme:error:badNonce" Api errors). The current value of retries in Client::post gives this Api error every 0.25% in every call to Client::post as part of Pebble testing.

This pull request increases the number of retries in Client::post from 3 to 10.

• In case 10 retries are reached, this indicates a bad ACME CA.
• To prevent an infinite loop an error is returned after 10 retries.
• There is no different behaviour for well behaved ACME CA with lower bad nonce probability
• The Pebble test is stable

[djc]

Sorry for the long delay in reviewing...

I don't think this is the right direction. This change affects both production and testing use, and I don't think this is a good change for production uses. Also, we should not change the value and the structure in the same commit.

[christianhoelzl]

Ok, fine, I'll close this pr. Pebble can also be tweaked with an env (PEBBLE_WFE_NONCEREJECT) to have less bad nonce responses while testing.