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] https://github.com/eventlet/eventlet/issues/534
[3] https://github.com/nameko/nameko/issues/655
[4] https://github.com/celery/kombu/issues/1082
[5] http://lists.openstack.org/pipermail/openstack-discuss/2019-August/008553.html

Change-Id: I113c06f6e09727aa279f5ab8d2b7534a019394c2

global-requirements.txt

@@ -111,7 +111,7 @@ pylev  # BSD
 pypowervm!=1.1.21,!=1.1.22  # Apache-2.0
 pyScss!=1.3.5  # MIT License
 django-pyscss  # BSD License (2 clause)
-kombu!=4.0.2  # BSD
+kombu!=4.0.2,!=4.6.4  # BSD
 ldap3  # LGPLv3
 deprecation  # Apache-2.0
 libvirt-python!=4.1.0,!=4.2.0  # LGPLv2+

upper-constraints.txt

@@ -530,7 +530,7 @@ openstacksdk===0.34.0
 six===1.12.0
 dulwich===0.19.12
 sentinels===1.0.0
-kombu===4.6.4
+kombu===4.6.3
 distro===1.4.0
 betamax-matchers===0.4.0
 yaql===1.1.3