Better integration tests for Python-based obfsproxy

obfsproxy integration tests are not robust.

• We need some integration tests that check how obfpsroxy works under different managed-mode environment variables.

• The obfsproxy/test/tester.py, which is our basic integration test, could use some love.

• I once started coding PITS, an advanced integration tester for obfsproxy. You can find the design docs here: https://gitweb.torproject.org/pluggable-transports/obfsproxy.git/blob/HEAD:/obfsproxy/test/int_tests/pits_design.txt Unfortunately, while I still like the idea, I'm not happy with its code. As a matter of fact, I have probably forgotten how it works and I should rip it off the obfsproxy codebase since it's pretty much useless.