Add --verify-server option

[blry]

Add --verify-server option which is used to force to renew a cert when ACME Directory Resource URI changes.

[Neilpang]

why need this ?

[blry]

I'll describe my case. We have an instance with CI/CD setup, and we don't have access using ssh. There's a shell script in Docker which runs every 6hours acme.sh with environment option for acme directory (e.g. $TESTING_ACME equals to --testing) to check if the certificate needs renew. In some time we decided to use real certificate, however when we disabled TESTING_ACME variable to generate certificate with real CA, it responded that actual certificate renew will be in a month.

Theoretically there was an option to make a commit with acme.sh --force and then reverse it, but it's not a good practice