Python 2 will reach end of life in January 1 2020.  Declare it as
deprecated.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20190503193721.18459-1-ehabkost@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
[ehabkost: print "warning:" in lowercase]
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>