Redis reset issues

[Olivier Sallou]

in some cases, mongo and redis may be out of sync. At scheduler restart, if running jobs queue in redis is not empty, databases are not resynced. Workaround is:

• stop scheduler and watchers
• clean in redis god:jobs key
• restart scheduler and watchers

[Olivier Sallou]

at restart, scheduler should clean the job queue in redis and resync it with expected jobs from mongo. Should care that scheduler is the master scheduler. Slave schedulers (for HA, in standby) should not try any resync.

[Olivier Sallou]

Closes #50, resync redis with mongo at each scheduler startup

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