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: I2826ded6a4be7507fc61e68fe6d9204682382252
Signed-off-by: Sean McGinnis <961eeb09b6d45516665e15b82e013282c4faf575@gmail.com>

openstack/oslo.db,openstack/oslo.db