Add py38 package metadata
Add py38 package metadata

Now that we are running the Victoria tests that include a
voting py38, we can now add the Python 3.8 metadata to the
package information to reflect that support.

Change-Id: I98566be10eec15ca3eaf795fb3717ac87f86632d
Signed-off-by: Sean McGinnis <961eeb09b6d45516665e15b82e013282c4faf575@gmail.com>

openstack/python-vitrageclient