Zuul status page: Clean up status.js

* Use dot notatation instead of bracket notation with string literals
* Strict comparison
* Missing semicolons
* Scope of 'html' variable in asynchronous action
* Chain jQuery method instead of re-selecting the same css
  selector from the DOM:
  $(foo).bar(); $(foo).quux(); -> $(foo).bar().quux();
* Use .empty() instead of .html('')
* Use .text() for text instead of .html()
  .html will trigger html parser where text will simply create
  a text node with the string literal, much faster, safer and
  semantically correct.
* Consistently use single quotes.
* Fix implied global variable leak 'result'.

Change-Id: I44231de5297ce21c1c4408ae7443ef1cab7dd41e
Zuul status page: Fix reference error that crashes/freezes the page

* Property data.trigger_event_queue and data.trigger_event_queue
  can be undefined, in which case data.trigger_event_queue.length
  causes an uncaught TypeError to be thrown.

Change-Id: I7cf6799869c6fdd9765062737114984f38bfb12d