Respend relay updates to support refactoring

Update doublespendrelay.py for test framework changes
Without this line, I get 
```
dgenr8@dgenr8-VirtualBox:~/bitcoinxt/qa/rpc-tests$ ./doublespendrelay.py 
Initializing test directory /tmp/testiOPuUb
Unexpected exception caught during testing: Insufficient funds: need 144, have 0
```