[pymongo] Fix multiple host kwarg

[Kyle-Verhoog]

Overview

This PR adds a fix for the bug demonstrated in #369.

Background

Due to supporting deprecated code, a hack existed that used the first argument passed to the TracedMongoClient. The first argument passed to MongoClient was host. This bug would occur when host was provided explicitly as a kwarg.

[Kyle-Verhoog]

dd-trace-py/ddtrace/contrib/pymongo/client.py

Lines 25 to 34 in 1797434

	@deprecated(message='Use patching instead (see the docs).', version='1.0.0')
	def trace_mongo_client(client, tracer, service=mongox.TYPE):
	tracer.set_service_info(
	service=service,
	app=mongox.TYPE,
	app_type=AppTypes.db,
	)
	traced_client = TracedMongoClient(client)
	ddtrace.Pin(service=service, tracer=tracer).onto(traced_client)
	return traced_client

We should consider moving this since it is the reason why the bug exists and this workaround fix is needed.