Clean up write commands support PYTHON-554

A few changes:

- Eliminate the ordered parameter - no reason this needs to be a
separate param.
- Use integers to represent the operation instead of strings - this
will make part of the bulk API implementation a bit cleaner and
avoid a bunch of string comparisons.
- Clean up namespace and collection name handling in collection.py - No
need to create a bunch of new strings or do unnecessary string copies.
- Pass client.disconnect to _check_command_response to deal with
"not master".