Update git submodules

* Update requirements from branch 'master'
  - Blacklist kombu-4.6.4
    
    Commit [1] bumped the upper constraint for kombu to 4.6.4. Per issues
    [2][3] this interacts poorly with eventlet and breaks many things
    openstack on py37 (including nova gate - see the linked bug) with this
    error:
    
    TypeError: open: path should be string, bytes or os.PathLike, not _NormalAccessor
    
    I opened an issue against kombu [4].
    
    It is possible there will be a simple way to fix those many things, but
    in the meantime, this commit blacklists 4.6.4 to get the world moving
    again.
    
    Thanks to Daniel Leaberry for doing the legwork to identify the problem
    [5].
    
    Closes-Bug: #1840551
    
    [1] Id71496bcb5c8342851f287e35931431e8a443d23
    [2] eventlet/eventlet#534
    [3] nameko/nameko#655
    [4] celery/kombu#1082
    [5] http://lists.openstack.org/pipermail/openstack-discuss/2019-August/008553.html
    
    Change-Id: I113c06f6e09727aa279f5ab8d2b7534a019394c2