[REST-TEST] Add master_timeout to the rest API specs

This change adds the parameter `master_timeout` to the rest requests that can write to a watch PUT, ACK and DELETE.
Also add support in the rest tests to verify that this is accepted.

Fixes: elastic/elasticsearch#416

Original commit: elastic/x-pack-elasticsearch@4cc1c50f2c

rest-api-spec/api/watcher.ack_watch.json

@@ -13,6 +13,10 @@
         }
       },
       "params": {
+        "master_timeout": {
+          "type": "duration",
+          "description": "Specify timeout for watch write operation"
+        }
       }
     },
     "body": null

rest-api-spec/api/watcher.delete_watch.json

@@ -13,6 +13,10 @@
         }
       },
       "params": {
+        "master_timeout": {
+          "type": "duration",
+          "description": "Specify timeout for watch write operation"
+        }
       }
     },
     "body": null

rest-api-spec/api/watcher.put_watch.json

@@ -13,6 +13,10 @@
         }
       },
       "params": {
+        "master_timeout": {
+          "type": "duration",
+          "description": "Specify timeout for watch write operation"
+        }
       }
     },
     "body": {

rest-api-spec/test/ack_watch/10_basic.yaml

@@ -7,6 +7,7 @@
   - do:
       watcher.put_watch:
         id: "my_watch"
+        master_timeout: "40s"
         body:  > 
           {
             "trigger" : {

rest-api-spec/test/delete_watch/10_basic.yaml

@@ -7,6 +7,7 @@
   - do:
       watcher.put_watch:
         id: "my_watch"
+        master_timeout: "40s"
         body:  > 
           {
             "trigger": {

rest-api-spec/test/put_watch/10_basic.yaml

@@ -7,6 +7,7 @@
   - do:
       watcher.put_watch:
         id: "my_watch"
+        master_timeout: "40s"
         body:  > 
           {
             "trigger": {