[serverctl] fix db-dump
Since changeset af47954c1015 we would die with:
AttributeError: 'ServerMigrationHelper' object has no attribute 'repo'
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')