Merge changes Iafd263c7,I29300b6b,If8422986,Ied877cd6,If30d8ca4, ...

* changes:
  Register _handle_control_packet in a single place
  Migrate to use cert_acl instead of cert_acl_handle
  Remove cert_acl_data_stream from _open_channel, as it can be inferred
  Remove cert_acl_handle return value, as it was not really used
  Begin migrating L2capTest to use PyAclManager
  Begin PyL2cap, to make interfacing with l2cap facade easier
  Add Closable, to reduce repeated code
  Move captures & PyHci/PyAclManager to common cert
  Move common setup to setup_test & teardown_test
  Add IEventStream, so other subjects can use emit, etc
  Flesh out PyAclManager a little more
  Start PyAclManager, to simplify interaction with AclManager