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.

This allows the selectDatabase() and selectCollection() to be tested (PHPLIB-144).

If we've learned anything from the legacy driver, it's that options arrays will prove more flexible than nullable, positional arguments in the long run.

The legacy driver would return a comma-delimited list of host:port combinations; however, that would require __toString() to invoke topology discovery on new Manager instances. Returning the URI is less invasive.

See: PHPC-465, HHVM-129

See: PHPC-444, HHVM-117