[SIEM][Detection Engine] critical blocker bug fixes ancestor mapping

## Summary

* Fixes critical bug with ancestor mapping being object and not correct mappings.

Testing you should now be able to do operations and it will show up on KQL
<img width="1111" alt="Screen Shot 2020-01-28 at 9 33 59 AM" src="https://user-images.githubusercontent.com/1151048/73284943-86d03e80-41b2-11ea-93a4-0d648169d223.png">

<img width="1116" alt="Screen Shot 2020-01-28 at 9 33 22 AM" src="https://user-images.githubusercontent.com/1151048/73285062-b0896580-41b2-11ea-8dfd-6dafa7f28fa9.png">


### Checklist

Use ~~strikethroughs~~ to remove checklist items you don't feel are applicable to this PR.

~~- [ ] This was checked for cross-browser compatibility, [including a check against IE11](https://github.com/elastic/kibana/blob/master/CONTRIBUTING.md#cross-browser-compatibility)~~

~~- [ ] Any text added follows [EUI's writing guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses sentence case text and includes [i18n support](https://github.com/elastic/kibana/blob/master/packages/kbn-i18n/README.md)~~

~~- [ ] [Documentation](https://github.com/elastic/kibana/blob/master/CONTRIBUTING.md#writing-documentation) was added for features that require explanation or tutorials~~

~~- [ ] [Unit or functional tests](https://github.com/elastic/kibana/blob/master/CONTRIBUTING.md#cross-browser-compatibility) were updated or added to match the most common scenarios~~

~~- [ ] This was checked for [keyboard-only and screenreader accessibility](https://developer.mozilla.org/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Accessibility#Accessibility_testing_checklist)~~

### For maintainers

~~- [ ] This was checked for breaking API changes and was [labeled appropriately](https://github.com/elastic/kibana/blob/master/CONTRIBUTING.md#release-notes-process)~~

~~- [ ] This includes a feature addition or change that requires a release note and was [labeled appropriately](https://github.com/elastic/kibana/blob/master/CONTRIBUTING.md#release-notes-process)~~

x-pack/legacy/plugins/siem/server/lib/detection_engine/routes/index/signals_mapping.json

@@ -23,7 +23,20 @@
             }
           },
           "ancestors": {
-            "type": "object"
+            "properties": {
+              "rule": {
+                "type": "keyword"
+              },
+              "id": {
+                "type": "keyword"
+              },
+              "type": {
+                "type": "keyword"
+              },
+              "depth": {
+                "type": "long"
+              }
+            }
           },
           "rule": {
             "properties": {