Auth Mechanism Properties in the Connection String

Currently the python driver supports a single "auth mechanism property", gssapiServiceName, for use with the GSSAPI mechanism. The goal of this ticket is to support the forthcoming standard for specifying mechanism properties, authMechanismProperties. The syntax looks like:

authMechanismProperties=PROPERTY_NAME:PROPERTY_VALUE,PROPERTY_NAME2:PROPERTY_VALUE2

PyMongo will support the SERVICE_NAME property, replacing gssapiServiceName name with:

authMechanismProperties=SERVICE_NAME:<your service name>