[feature] bifrost waits for thorchain to catch up

When bifrost starts, and has no previous data, no start height set in the configuration file, then it queries for the block height of thorchain. But for a new node, that height is not the current block height as the chain needs time (hours, days, weeks) to catch up first.

This code change puts bifrost on hold until its thorchain node is caught up to the rest of the nodes.