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* [Enhancement] tox: Bump xblock12 env to XBlock 1.2.3
* [Enhancement] Add Python 3.7 to Travis configuration
* [Enhancement] tasks.py: continue on specific EnvironmentErrors during SSH connection
* [Enhancement] Update devstack documentation
* [Enhancement] Task hooks
* [DEPRECATION] `reboot_on_resume` will be removed in a future release, as its
intended purpose is now better served by task hooks.
* [CONFIGURATION] The `suspend_in_parallel` configuration option is now a NOOP,
as suspension now always happens in parallel via simultaneously running
Celery tasks.