This refactors the existing Database method to use an Operation class.

Parsing the "readconcernlevel" URI option depends on PHPC-523, so we'll skip those tests for now.

See: https://github.com/travis-ci/travis-ci/issues/5143

The driver (via libmongoc) already does this.

This reverts commit 451f72c4.

This should help avoid failed IPv6 connections when "localhost" resolves to an IPv6 literal and mongod does not have `net.ipv6}} enabled to listen for IPv6.