We couldn't copy to_unicode, to_bytes, to_str into module_utils because
of licensing. So once created it we had two sets of functions that did
the same things but had different implementations. To remedy that, this
change removes the ansible.utils.unicode versions of those functions.
* Use six instead of urllib2, for python 3 compat
* Open the certificate file using binary mode
On python3, os.write requires 'bytes'. Also avoid
using a too broad exception, since the issue was hard
to spot due to it.
* Do not add the header User-agent if not set
Python3 module do raise a exception if a header is
not a string-like object, and the default value is None.