Check default retention configuration

[mohierf]

Without any configuration since the default configuration, I got:

[2019-04-16 13:41:32] INFO: [scheduler-master.alignak.module.inner-retention] Loading retention data from 1 files
[2019-04-16 13:41:32] INFO: [scheduler-master.alignak.module.inner-retention] Supposed retention file /tmp/alignak-retention-scheduler-master.json is not correctly encoded! Got: {u'north_host_009': {u'last_time_unreachable': 0, u'flapping_changes': [], u'active_checks_enabled': True, u'in_scheduled_downtime_during_last_check': False, u'last_perf_data': u'', u'state_before_hard_unknown_reach_phase': u'UP', u'last_event_id': 0, u'process_perf_data': True, u'in_hard_unknown_reach_phase': False, u'problem_has_been_acknowledged': False, u'current_notification_number': 0, u'last_problem_id': 0, u'should_be_scheduled': 1, u'notifications_in_progress': {}, u'notified_contacts': [], u'freshness_expired': False, u'last_notification': 0, u'check_flapping_recovery_notification': True, u'last_state': u'UP', u'latency': 0.8317360877990723, u'passive_checks_enabled': True, u'start_time': 0, u'pending_flex_downtime': 0, u'last_state_type': u'HARD', u'downtimes': {}, u'last_time_up': 1555413789, u'last_hard_state': u'UP', u'next_chk': 1555414688, u'percent_state_change': 0.0, u'state': u'UP', u'comments': {},