Impacted versions:
9.0, 10.0, 11.0 (Maybe 8.0)
I don't know if it is really an expected behaviour for odoo but I like to expose it

Steps to reproduce:

1. Open an ir.cron record and change it to:
 - interval: minutes
 - next execution date: now + 1 minute

2. Open the odoo server log

Note: I'm using workers=3 but I don't know if there is possible to reproduce it without workers.

Current behavior:

You will see for each cron execution the following output
```txt
...
2018-06-01 16:18:33,432 20686 INFO 333561-11-0-42aff9-all odoo.modules.registry: Invalidating all model caches after database signaling.
...
2018-06-01 16:17:21,527 20687 INFO 333561-11-0-42aff9-all odoo.modules.loading: loading 1 modules...
2018-06-01 16:17:21,535 20687 INFO 333561-11-0-42aff9-all odoo.modules.loading: 1 modules loaded in 0.01s, 0 queries
2018-06-01 16:17:21,594 20687 INFO 333561-11-0-42aff9-all odoo.modules.loading: loading 206 modules...
2018-06-01 16:17:21,718 20687 INFO 333561-11-0-42aff9-all odoo.modules.loading: 206 modules loaded in 0.12s, 0 queries
2018-06-01 16:17:21,989 20687 INFO 333561-11-0-42aff9-all odoo.modules.loading: Modules loaded.
```

Expected behavior:
 - Review if the method that run from the cron really requires a invalidate cache and delete all registries.
 - Disable "minutes" for cron interval because all cache are deleted then is not valid use them.

Video/Screenshot link (optional):

 - [![IMAGE ALT TEXT HERE](https://img.youtube.com/vi/Be4FIeQjgjk/0.jpg)](https://youtu.be/Be4FIeQjgjk)
if sig in [signal.SIGINT, signal.SIGTERM]:
            
            self.quit_signals_received += 1
            if self.quit_signals_received > 1:
                
                sys.stderr.write("Forced shutdown.\n")
                os._exit(0)
        elif sig == signal.SIGHUP:
            
            openerp.phoenix = True
            self.quit_signals_received += 1
    def cron_thread(self, number):
        while True:
            time.sleep(SLEEP_INTERVAL + number)     
            registries = openerp.modules.registry.RegistryManager.registries
            _logger.debug('cron%d polling for jobs', number)
            for db_name, registry in registries.iteritems():
                while registry.ready:
                    try:
                        acquired = openerp.addons.base.ir.ir_cron.ir_cron._acquire_job(db_name)
                        if not acquired:
                            break
                    except Exception:
                        _logger.warning('cron%d encountered an Exception:', number, exc_info=True)
                        break
    def cron_spawn(self):