[eslint] remove exception for prefer-const, and fix violations

.eslintrc.yaml

@@ -1,5 +1,2 @@
 ---
 extends: "@elastic/eslint-config-kibana"
-
-rules:
-  prefer-const: warn

src/lib/connection.js

@@ -55,13 +55,12 @@ ConnectionAbstract.prototype.ping = function (params, cb) {
   let requestTimeout = this.pingTimeout;
   let requestTimeoutId;
   let aborted;
-  let abort;
 
   if (params && params.hasOwnProperty('requestTimeout')) {
     requestTimeout = params.requestTimeout;
   }
 
-  abort = this.request(_.defaults(params || {}, {
+  const abort = this.request(_.defaults(params || {}, {
     path: '/',
     method: 'HEAD'
   }), function (err) {

src/lib/connectors/http.js

@@ -133,11 +133,11 @@ HttpConnector.prototype.makeReqParams = function (params) {
 HttpConnector.prototype.request = function (params, cb) {
   let incoming;
   let timeoutId;
-  let request;
   let status = 0;
   let headers = {};
   const log = this.log;
   let response;
+  let request; // eslint-disable-line prefer-const
 
   const reqParams = this.makeReqParams(params);
 

test/integration/yaml_suite/yaml_doc.js

@@ -449,7 +449,7 @@ YamlDoc.prototype = {
       catcher = null;
     }
 
-    let timeoutId;
+    let timeoutId; // eslint-disable-line prefer-const
     const cb = _.bind(function (error, body) {
       this._last_requests_response = body;
       clearTimeout(timeoutId);