sync_with_ping currently returns false if the timeout expires, and it is
the caller's responsibility to fail the test. However, none of the tests
currently assert on sync_with_ping()'s return code. This commit adds an
assert to sync_with_ping so the test will fail if the timeout expires.
This commit also removes all the duplicate implementations of
sync_with_ping() from the individual tests.
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.
