Fix deleteUser with RestHelper on cluster without redis

12:20:25 userCanChangeItsOwnPassword(org.nuxeo.ftest.cap.ITUsersTest)  Time elapsed: 22.045 sec  <<< ERROR!
12:20:25 org.nuxeo.client.internals.spi.NuxeoClientException: null
12:20:25 	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
12:20:25 	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
12:20:25 	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
12:20:25 	at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
12:20:25 	at com.fasterxml.jackson.databind.introspect.AnnotatedConstructor.call1(AnnotatedConstructor.java:119)
12:20:25 	at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromString(StdValueInstantiator.java:291)
12:20:25 	at com.fasterxml.jackson.databind.deser.std.ThrowableDeserializer.deserializeFromObject(ThrowableDeserializer.java:111)
12:20:25 	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:133)
12:20:25 	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3807)
12:20:25 	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2797)
12:20:25 	at org.nuxeo.client.api.marshaller.NuxeoConverterFactory.readJSON(NuxeoConverterFactory.java:100)
12:20:25 	at org.nuxeo.client.api.objects.NuxeoEntity.getResponse(NuxeoEntity.java:145)
12:20:25 	at org.nuxeo.client.api.objects.user.UserManager.deleteUser(UserManager.java:81)
12:20:25 	at org.nuxeo.functionaltests.RestHelper.deleteUser(RestHelper.java:164)
12:20:25 	at org.nuxeo.ftest.cap.ITUsersTest.after(ITUsersTest.java:55)

10:45:36 Running org.nuxeo.ftest.cap.ITSearchTabTest
10:46:18 Tests run: 1, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 42.164 sec <<< FAILURE! - in org.nuxeo.ftest.cap.ITSearchTabTest
10:46:18 testSearch(org.nuxeo.ftest.cap.ITSearchTabTest)  Time elapsed: 39.167 sec  <<< FAILURE!
10:46:18 java.lang.AssertionError: null
10:46:18 	at org.junit.Assert.fail(Assert.java:86)
10:46:18 	at org.junit.Assert.assertTrue(Assert.java:41)
10:46:18 	at org.junit.Assert.assertTrue(Assert.java:52)
10:46:18 	at org.nuxeo.ftest.cap.ITSearchTabTest.after(ITSearchTabTest.java:125)