Fix SNI check when custom root-CA used on Apple devices.

Validate hostname on Mac when custom root-CA is used. (#396)

**Issue:** When custom root-CA was specified, we were not validating hostname.

**Solution:** Use `SecPolicyCreateSSL()` instead of `SecPolicyCreateBasicX509()` in this scenario.

**Also:**
1) The lifetime of `unittests.crt` had to be shortened to 2.25 years to meet the [stricter standards](https://support.apple.com/en-us/HT210176) of `SecPolicyCreateSSL()`. Added `unittests.readme` with instructions on how to update these files again in the future.

2) Simplify code that logs the server name. (The code we had didn't actually do what we thought it did. As far as I can tell SecureChannel API doesn't offer a function to query the server name)

Credit: Adapted from patch submitted by F-Secure