Batfish: fix leak in checkConfiguration
Batfish: fix leak in checkConfiguration

This is for batfish/batfish#172

intentionet/batfish,arifogel/batfish,intentionet/batfish,dhalperi/batfish,intentionet/batfish,dhalperi/batfish,batfish/batfish,arifogel/batfish,arifogel/batfish,dhalperi/batfish,intentionet/batfish,batfish/batfish,intentionet/batfish,batfish/batfish