Adding pid info to servers allows matching coredumps with servers
Other improvements:
- When replacing just some fields of ServerInfo, use `_replace` instead of
building a new object. This way it is agnostic to changes to the Object
- When building ServerInfo from a list, the types defined for its fields are
not enforced, so ServerInfo(*list) works fine and does not need to be changed if
fields are added or removed.
We adjust all of the simple cases of cluster tests so they work
with `rf_rack_valid_keyspaces: true`. It boils down to assigning
nodes to multiple racks. For most of the changes, we do that by:
* Using `pytest.mark.prepare_3_racks_cluster` instead of
`pytest.mark.prepare_3_nodes_cluster`.
* Using an additional argument -- `auto_rack_dc` -- when calling
`ManagerClient::servers_add()`.
In some cases, we need to assign the racks manually, which may be
less obvious, but in every such situation, the tests didn't rely
on that assignment, so that doesn't affect them or what they verify.
Add sleep before starting gossiper to increase a chance of getting old
gossiper entry about yourself before updating local gossiper info with
new IP address.
