Search .kibana-devnull rather than -*

There are too many edge cases when using shield and searching against
the index pattern -*, some of which seem impractical to resolve in the
short term. Instead, we query against the non-existent index
.kibana-devnull, which the default kibana privileges in shield will
allow.

Note: This assumes that .kibana-devnull either does not exist or is
empty.

Fixes #5765

src/ui/public/courier/fetch/strategy/__tests__/search.js

@@ -103,11 +103,11 @@ describe('ui/courier/fetch/strategy/search', () => {
     context('when indexList is empty', () => {
       beforeEach(() => reqsFetchParams[0].index = []);
 
-      it('explicitly negates any indexes', () => {
+      it('queries .kibana-devnull instead', () => {
         let value;
         search.reqsFetchParamsToBody(reqsFetchParams).then(val => value = val);
         $rootScope.$apply();
-        expect(_.includes(value, '"index":["-*"]')).to.be(true);
+        expect(_.includes(value, '"index":[".kibana-devnull"]')).to.be(true);
       });
     });
   });

src/ui/public/courier/fetch/strategy/search.js

@@ -57,7 +57,7 @@ define(function (require) {
             // handle that request by querying *all* indexes, which is the
             // opposite of what we want in this case.
             if (_.isArray(indexList) && indexList.length === 0) {
-              indexList.push('-*');
+              indexList.push('.kibana-devnull');
             }
             return angular.toJson({
               index: indexList,