Create function wait_for_gossip

[czarte]

Create function wait_for_gossip, that ensures the Gossip process is over to perform requests for web content in tests.

In this moment we are just starting and shutting down the nodes in the multinode integration test, because the process of starting and shutting down the cluster of the nodes, because the process was quick enough to process gossips immediately. So construction of the neighborhood was fast enough to process requests in such a short time in tests. In GH-788 we implemented construction of CountryBlocks into the memory, so node is starting bit delayed and we need to wait a bit for gossip to process and construct Neighborhood, so we need to check if nodes already created the Patch to successfully perform the request in the multinode tests.

multinode_integration_tests/tests/bookkeeping_test.rs