CDRIVER-4207 handshake on new stream in scanner

[kevinAlbs]

Summary

Always send the full connection handshake as the first command on a stream in single-threaded monitoring. The bug described in CDRIVER-4207 results in a monitoring command as the first command.

Rejected ideas

I rejected the idea of setting last_failed in mongoc_topology_scanner_node_disconnect. last_failed is used to apply cooldownMS in mongoc_topology_scanner_node_in_cooldown. The Server Monitoring spec does not say that cooldownMS should apply when a network error occurs on an application operation.

[jmikola]

Tested this patch with PHPLIB's test suite (PHPLIB-717) and noted that we no longer receive the following errors throughout:

Failed to get handshake server description: Driver attempted to initialize in load balancing mode, but the server does not support this mode.

[chardan]

+1, this looks good! (In my current changes, I'm also having to add more parameters to this function, I'm starting to wonder if it's worth an "options" parameter or something.)