[test] pull yapps from Logilab's github
Fixes a couple of failures, pull request is almost a year old
(https://github.com/smurfix/yapps/pull/2).
change_attribute_type('CWCache', 'timestamp', 'TZDatetime')
change_attribute_type('CWUser', 'last_login_time', 'TZDatetime')
change_attribute_type('CWSource', 'latest_retrieval', 'TZDatetime')
drop_attribute('CWSource', 'synchronizing')
add_attribute('CWSource', 'in_synchronization')