Ordered test generators were not announced in plugin hooks, so
e.g. the Beakerlib or collect plugin did not announce them.
Exclude test generators from ordering.
Tests in test classes decorated by @ipatests.order_plugin.ordered
are sorted by the source line number instead of alphabetically,
if the plugin is enabled.
The ipa-run-tests helper now loads and enables the plugin.
This should make writing integration tests easier.
Petr Viktorin