Fix random ftest error log on NXAuditEventsService

[2021-01-29T17:55:21.894Z] /home/jenkins/workspace/nuxeo_nuxeo_PR-4609/ftests/nuxeo-server-hotreload-tests/target/tomcat/log/server.log:
[2021-01-29T17:55:22.530Z] 2021-01-29T17:50:00,486 ERROR [Quartz_Worker-1] [org.nuxeo.ecm.platform.audit.service.NXAuditEventsService] Can not provide service org.nuxeo.ecm.platform.audit.api.AuditLogger since backend is undefined
[2021-01-29T17:55:22.533Z] 2021-01-29T17:50:00,502 ERROR [Nuxeo-Work-updateACEStatus-1:16557397249371.1342491637] [org.nuxeo.ecm.platform.audit.service.NXAuditEventsService] Can not provide service org.nuxeo.ecm.platform.audit.api.AuditLogger since backend is undefined
[2021-01-29T17:55:22.534Z] 2021-01-29T17:50:00,512 ERROR [Quartz_Worker-1] [org.nuxeo.ecm.platform.audit.service.NXAuditEventsService] Can not provide service org.nuxeo.ecm.platform.audit.api.AuditLogger since backend is undefined

[2021-02-02T21:25:27.224Z] /home/jenkins/workspace/nuxeo_nuxeo_PR-4609/ftests/nuxeo-csv-ftests/target/tomcat/log/server.log:
[2021-02-02T21:25:27.225Z] 2021-02-02T21:00:00,074 ERROR [Quartz_Worker-1] [org.nuxeo.ecm.platform.audit.service.NXAuditEventsService] Can not provide service org.nuxeo.ecm.platform.audit.api.AuditLogger since backend is undefined

[2021-02-03T23:31:31.763Z] /home/jenkins/workspace/nuxeo_nuxeo_PR-4614/ftests/nuxeo-cas2-login-ftests/target/tomcat/log/server.log:
[2021-02-03T23:31:31.763Z] 2021-02-03T23:05:00,050 ERROR [Quartz_Worker-1] [org.nuxeo.ecm.platform.audit.service.NXAuditEventsService] Can not provide service org.nuxeo.ecm.platform.audit.api.AuditLogger since backend is undefined
[2021-02-03T23:31:31.770Z] 2021-02-03T23:05:00,224 ERROR [Quartz_Worker-1] [org.nuxeo.ecm.platform.audit.service.NXAuditEventsService] Can not provide service org.nuxeo.ecm.platform.audit.api.AuditLogger since backend is undefined
[2021-02-03T23:31:31.771Z] 2021-02-03T23:05:00,226 ERROR [Nuxeo-Work-updateACEStatus-1:32587775077407.2090567634] [org.nuxeo.ecm.platform.audit.service.NXAuditEventsService] Can not provide service org.nuxeo.ecm.platform.audit.api.AuditLogger since backend is undefined

[2021-02-04T23:56:37.923Z] [Text Finder] Searching for pattern '.*ERROR.*' in file set 'ftests/**/log/server.log'...[2021-02-04T23:56:38.041Z] /home/jenkins/workspace/nuxeo_nuxeo_PR-4626/ftests/nuxeo-audit-storage-directory-ftests/target/tomcat/log/server.log:[2021-02-04T23:56:38.042Z] 2021-02-04T23:30:00,078 ERROR [Quartz_Worker-1] [org.nuxeo.ecm.platform.audit.service.NXAuditEventsService] Can not provide service org.nuxeo.ecm.platform.audit.api.AuditLogger since backend is undefined[2021-02-04T23:56:38.042Z] 2021-02-04T23:30:00,114 ERROR [Quartz_Worker-1] [org.nuxeo.ecm.platform.audit.service.NXAuditEventsService] Can not provide service org.nuxeo.ecm.platform.audit.api.AuditLogger since backend is undefined[2021-02-04T23:56:38.043Z] 2021-02-04T23:30:00,353 ERROR [Quartz_Worker-1] [org.nuxeo.ecm.platform.audit.service.NXAuditEventsService] Can not provide service org.nuxeo.ecm.platform.audit.api.AuditLogger since backend is undefined[2021-02-04T23:56:38.043Z] 2021-02-04T23:30:00,357 ERROR [Quartz_Worker-1] [org.nuxeo.ecm.platform.audit.service.NXAuditEventsService] Can not provide service org.nuxeo.ecm.platform.audit.api.AuditLogger since backend is undefined[2021-02-04T23:56:38.044Z] 2021-02-04T23:30:00,357 ERROR [Nuxeo-Work-updateACEStatus-1:52398296422349.1474189521] [org.nuxeo.ecm.platform.audit.service.NXAuditEventsService] Can not provide service org.nuxeo.ecm.platform.audit.api.AuditLogger since backend is undefined[2021-02-04T23:56:38.044Z] 2021-02-04T23:30:00,368 ERROR [Quartz_Worker-1] [org.nuxeo.ecm.platform.audit.service.NXAuditEventsService] Can not provide service org.nuxeo.ecm.platform.audit.api.AuditLogger since backend is undefined[2021-02-04T23:56:39.159Z] [Text Finder] Finished searching for pattern '.*ERROR.*' in file set 'ftests/**/log/server.log'.[2021-02-04T23:56:39.159Z] [Text Finder] Setting build result to 'FAILURE'.