Add support for passing SSL context to urllib

[JoakimSoderberg]

This can be useful when testing towards a Jenkins instance with a selfsigned SSL certificate.

Specifically I would like to add a command line option --no-check-certificate to jenkins-job-builder just like tools like curl / wget has.

This would then be used like this to turn off the verification of the certificate:

ctx = ssl.create_default_context()
ctx.check_hostname = False
ctx.verify_mode = ssl.CERT_NONE

server = jenkins.Jenkins('https://jenkins.local', ssl_context=ctx)

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