Revert "tests: Support calling add_nodes more than once"
Revert "tests: Support calling add_nodes more than once"

This reverts commit 98a1846b00d9c3076d6dcd96244fae6f923e26a0.

chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin