fix(redis): add default values

Author: dszakallas

lib/instrumentations/redis.js

@@ -26,7 +26,7 @@ module.exports = function wrap (redis, agent, pkg) {
             var commands = this.__trace
             return utils.wrapQuery.call(this, originalExec, args, agent, {
               protocol: consts.PROTOCOLS.REDIS,
-              host: host,
+              host: host || 'unknown',
               method: 'multi: ' + commands.join(', '),
               url: 'unknown'
             })
@@ -35,7 +35,7 @@ module.exports = function wrap (redis, agent, pkg) {
         } else {
           return utils.wrapQuery.call(this, original, args, agent, {
             protocol: consts.PROTOCOLS.REDIS,
-            host: host,
+            host: host || 'unknown',
             method: name,
             url: 'unknown'
           })