Allow offline integ tests to be run in a no-network/firewalled state

Stem's integration tests are run by e.g. run_tests.py --all or tox, and by default do not include the ONLINE target. (See run_tests.py --help for more info on running ONLINE tests.)

These remaining integration tests should be runnable offline; however, it appears that they require the tor process to bootstrap to 5% in order to run. Waiting for 5% was introduced in commit fbfa73a099d9645f18d9846420cbf0145065b11d from 2011.

Empirically, I switched this to 0% and all these integ tests still worked fine.

In chatting with atagar over IRC, he wasn't aware of a reason offhand for waiting for 5%, and suggested we could change this since the tests still pass.