Fix SSL problems for old versions of Python 2.7.x

[andreagrandi]

Hi,

with this patch we solved the connection probelms with urls using SSL when using an old version of Python, such as:

/usr/lib/venv/local/lib/python2.7/site-packages/requests/packages/urllib3/util/ssl_.py:122: InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. You can upgrade to a newer version of Python to solve this. For more information, see https://urllib3.readthedocs.io/en/latest/security.html#insecureplatformwarning.

[metaodi]

are all of these required? I can't see anything in the code about idna, ndg-httpsclient, pyasn1 and enum34

[andreagrandi]

idna for example is needed by pyOpenSSL https://github.com/urllib3/urllib3/blob/master/src/urllib3/contrib/pyopenssl.py#L11
the others I'm not sure about. I'm porting changes my team did in the last 2 years https://github.com/datagovuk/ckanext-harvest/commits/2.0 in a for we have and we would really love to merge these back upstream. Do you have any suggestion about how I could check if the other mentioned dependencies may not be needed? Thanks

[andreagrandi]

Ok, we did more investigations on this and these are our findings:

• enum34==1.1.6 and idna==2.7 are being installed by pyOpenSSL==18.0.0 (which we need to fix this TLS problem)
• urllib3==1.23 is installed by requests

This leaves us with ndg-httpsclient==0.5.1 and pyasn1==0.4.4 which we are still not sure about. I will update this PR in the mean time and try to remove those libs from our environment to check if any other dependency is touched.

Cheers

[andreagrandi]

All right, I've removed the dependencies that were not needed. How does it look now? Cheers

[metaodi]

@andreagrandi Thank you very much!