Add dependencies needed by python requests for SNI support

The default python requests library for python2 is not able to handle
SNI enabled sites (sites with multiple https configurations per IP, see
https://en.wikipedia.org/wiki/Server_Name_Indication for more info).

To correct this, one needs to install pyOpenSSL, ndg-httpsclient and
pyasn1 (recommended packages for urllib3 in some distros, e.g. debian -
https://packages.debian.org/sid/python-urllib3 )