Fix dependency error
Fix dependency error

The 4.0.0 version of kombu (transitive dependency from oslo_messaging)
has a dependency issue, causing tox runs to fail. This patch fixes the
version of kombu to the last known working version.

Signed-off-by: Thomas Bachman <3b105edac745e0adc9775fe581389edb5ec1cc85@yahoo.com>

noironetworks/apic-ml2-driver,noironetworks/apic-ml2-driver