Support custom list of SSL CAs

[okhoma]

Beyond corporate firewall it is sometimes needed to provide a list of additional certification authorities:

https://docs.python.org/3/library/urllib.request.html#urllib.request.urlopen

urllib.request.urlopen(url, data=None, [timeout, ]*, cafile=None, capath=None, cadefault=False, context=None)
...
The optional cafile and capath parameters specify a set of trusted CA certificates for HTTPS requests. cafile should point to a single file containing a bundle of CA certificates, whereas capath should point to a directory of hashed certificate files. More information can be found in ssl.SSLContext.load_verify_locations().

Add support for cafile and capath parameters.