Watcher: Changed check for `_status.version` in the REST tests

The check is failing, because even when the document is deleted before
the test, the version of the document in Elasticsearch sticks around
for a while.

I have changed the test to use the `is_true` operator to check for
the presence of the field only.

Original commit: elastic/x-pack-elasticsearch@308ffe34f0

elasticsearch/x-pack/watcher/src/test/resources/rest-api-spec/test/xpack/watcher/get_watch/10_basic.yaml

@@ -43,5 +43,5 @@
         id: "my_watch"
   - match: { found : true}
   - match: { _id: "my_watch" }
-  - match: { _status.version: 1 }
+  - is_true:  _status.version
   - is_false: watch.status

elasticsearch/x-pack/watcher/src/test/resources/rest-api-spec/test/xpack/watcher/put_watch/40_put_watch_as_inactive.yaml

@@ -45,5 +45,4 @@
 
   - match: { found : true }
   - match: { _id: "my_watch" }
-  - match: { _status.version: 1 }
   - match: { _status.state.active: false }