Resolves the following warnings seen in the likes of nova:
DeprecationWarning: Please provide `is_available()` function in your
custom Eventlet hub <module 'oslo_service' from
'../oslo_service/__init__.py'>."
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: I219cf652526802b8212fe8a8f6c499e9aa24a3cf
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>