uncap eventlet
uncap eventlet

We will manage the eventlet version using constraints now. See the
thread starting at
http://lists.openstack.org/pipermail/openstack-dev/2018-April/129096.html
for more details.

Change-Id: Id852a3e6c7f9ac39001618384ced8289c2e6866e
Signed-off-by: Doug Hellmann <0798ebecfb7bc4dfb9d0445c2fa030eb64e1fa1c@doughellmann.com>

openstack/oslo.db,openstack/oslo.db