[ML] Improve error on get calendar when ml-meta index is missing (elastic/x-pack-elasticsearch#3576)

Relates elastic/x-pack-elasticsearch#3016

Original commit: elastic/x-pack-elasticsearch@bc60a0cb72

plugin/core/src/main/java/org/elasticsearch/xpack/ml/job/persistence/JobProvider.java

@@ -51,6 +51,7 @@ import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentFactory;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.common.xcontent.XContentType;
+import org.elasticsearch.index.IndexNotFoundException;
 import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.index.query.BoolQueryBuilder;
 import org.elasticsearch.index.query.QueryBuilder;
@@ -1204,8 +1205,12 @@ public class JobProvider {
 
             @Override
             public void onFailure(Exception e) {
+                if (e instanceof IndexNotFoundException) {
+                    listener.onFailure(new ResourceNotFoundException("No calendar with id [" + calendarId + "]"));
+                } else {
                     listener.onFailure(e);
                 }
+            }
         },
         client::get);
     }

plugin/src/test/resources/rest-api-spec/test/ml/calendar_crud.yml

@@ -92,6 +92,13 @@
             "job_ids": ["cal-job", "unknown-job"]
           }
 
+---
+"Test get calendar given missing":
+  - do:
+      catch: /No calendar with id \[unknown\]/
+      xpack.ml.get_calendars:
+        calendar_id: "unknown"
+
 ---
 "Test PageParams":
   - do:

qa/smoke-test-ml-with-security/build.gradle

@@ -20,6 +20,7 @@ integTestRunner {
     'ml/ml_classic_analyze/Test analyze API with an analyzer that does what we used to do in native code',
     // Remove tests that are expected to throw an exception, because we cannot then
     // know whether to expect an authorization exception or a validation exception
+    'ml/calendar_crud/Test get calendar given missing',
     'ml/calendar_crud/Test cannot create calendar with name _all',
     'ml/calendar_crud/Test PageParams with ID is invalid',
     'ml/calendar_crud/Test post calendar events given empty events',