Hosting integration test

And lots of race condition fixes along the way (benign ones, for the most part). This also required adding a configurable duration to the /renter/upload call, which in turn required adding a new field to renter.json...more than I would have liked, but compatibility should be ok. The repair scheme now works like this (in theory): if you manually pass in a duration, the renter will calculate the resulting ending height and use that for all future contracts for that file. So if you specify duration=10 at height 100, whenever the renter repairs the file, it will create contracts ending at height 110, and remove the file from the repair set after that height has been reached. But if you don't supply a duration (or if duration=0), the renter will renew the file indefinitely. Reasonable?