This commit adjusts the backwards compatability test in 2 ways:
1) we first set up the bitcoin backend before waiting for our network
nodes to start. This is so that the nodes can sync to chain and
become fully active during the `wait_for_nodes` call.
2) Then, in the `wait_for_node` helper, we use the status server
response to determine if a node is ready instead of just waiting for
`GetInfo` to return a response. This is because waiting for
SERVER_ACTIVE is a more accurate signal that the node is ready to
receive RPC calls.
