feat(pool): add support for resetting the connection pool
feat(pool): add support for resetting the connection pool

SDAM requires us to be able to rest the connection pool in certain
conditions, but we have traditionally not done this in the node
driver. This implements support for the reset, and unblocks us from
implementing tests like "cursors survive primary stepdown"

NODE-1682

mongodb/node-mongodb-native,mongodb/node-mongodb-native,mongodb/node-mongodb-native,mongodb/node-mongodb-native