commit 159fe88abfadf67410578c145e631819cf50b660
Author: John Newbery <john@johnnewbery.com>
Date:   Tue Mar 28 13:41:22 2017 -0400

    Remove SingleNodeConnCB

    This commit merges the NodeConnCB and SingleNodeConnCB into a single
    class (called NodeConnCB). The original intent for the NodeConnCB was to
    be able to have a python 'mininode' connect to multiple running
    bitcoinds. This has never been used and can be achieved more easily by
    having multiple NodeConns backed by a common datastore if it is ever
    needed.

    The changes in mininode.py are just code moves (and merging the two
    classes into a single class). The code changes in the individual test
    cases are changing the subclasses to subclass from NodeConnCB instead of
    SingleNodeConnCB. There is a lot of duplicate code in the subclasses
    that can be removed in future commits.