Update Cloudomate to Python3 and add VPN support

The changes introduced by this PR:

Python 3 migration
Electrum dependency updated to the default python 3 variant
Mechanicalsoup instead of Mechanize
Added VPN support with AzireVPN as currently implemented provider
Added integration tests for all VPS providers (to test for breakage of purchase interaction)
Added a randomuser option to retrieve and use random user data from www.fakeaddressgenerator.com
Added VPSOutOfStockException to denote when a VPS is out of stock

Tribler / cloudomate