Bug fix for #2334.
On server start, clear is_running on any old chronograph jobs.
Required import for clearing of is_running on Jobs.
Merge pull request #2337 from cpauya/feature/2334-Cannot-sync-server-on-Mac-to-central-server

Bug fix for #2334.
Increase sleep time in test_delete_group test, to try to help Travis.
Merge branch 'release-0.12.0' of github.com:learningequality/ka-lite into release-0.12.0
Merge release-0.12.0 to branch.