An automated test for checking that a PR can sync

As part of the automated travis build (or maybe it could be a separate thing from travis) , we should try to run and sync the built lbrycrd on testnet to see if it can a) sync from scratch and b) start up when its already synced and can succesfuly recieve a couple of blocks.

Not sure if this is possible just using travis (might take too long? use too much disk space?). We might have to set up some servers for this.