[test] run unittest_migractions on postgresql
sqlite's lack of support for a bunch of alter table functionality means
some thing just don't get tested otherwise.
option_group_changed('port', 'main', 'web')
option_group_changed('query-log-file', 'main', 'web')
option_group_changed('profile', 'main', 'web')
option_group_changed('max-post-length', 'main', 'web')