Update bch testnet seeds

[imaginaryusername]

liteco.in is not longer responsive; also joins current network on testnet.imaginary.cash

[jtoomim]

I prefer to keep PERSIST=False for testnets. That way, you'll join an existing p2pool network if one exists with those seeds (or with manually added nodes), but if you can't find any peers, you'll still be able to create your own chain and do your tests.