Resolves the following warnings seen in the likes of Neutron:
opt/stack/neutron/neutron/common/eventlet_utils.py:28:
DeprecationWarning: Please provide `is_available()`
function in your custom Eventlet hub <module 'oslo_service'
It must return bool: whether hub supports current platform. See
eventlet/hubs/{epoll,kqueue} for example.
Since we're simply taking the default hub provided by eventlet and
overriding a single attribute, we will always have support so set the
attribute.
Change-Id: Ie90bcce1d1724108e5d0e583a36aa2e20102bba4
f9b5a7b6d7