Issue with centers with intermediate step

[jaumann]

For some centers that are close together (BWI & IAD for example) there is an additional page that you are directed to after selecting the center. This breaks the flow in phantom. The page you are redirected to is https://goes-app.cbp.dhs.gov/main/goes/SelectEnrollmentCenterPostAction.do, which gives you an option to select another close by center.

Steps to reproduce:

1. Set 7940 as the enrollment center (BWI)
2. Run phantomjs ge-cancellation-checker.phantom.js -v
3. Observe error

phantomjs ge-cancellation-checker.phantom.js -v
Please wait...
On GOES login page...
Logging in...
Accepting terms...
Entering appointment management...
Entering rescheduling selection page...
Choosing Location: Baltimore Enrollment Center - Baltimore Washington Thurgood Marshall I, Lower Level Door 18, Linthicum, MD 21240, US
Error on page: TypeError: null is not an object (evaluating 'document.querySelector('.date table tr:first-child td:first-child').innerHTML')

[EpochalEngineer]

@apendleton @davidofwatkins Can this be merged in?

Applying the commit diff works as of the current git HEAD

[apendleton]

@EnviousElitist I had no way to test against locations that don't have this behavior, so I can't be certain it doesn't break things for non-DC-area people. If someone can confirm that, though, then yeah.

[EpochalEngineer]

@apendleton I should've mentioned I did indeed verify it worked with another enrollment center. You can simply modify config.json and throw in a new enrollment center. I used 9200 for PIT, feel free to verify yourself. Though I suppose that scheduling may not be available to you if you're not at that stage in the process, if that's what you meant.

Note that the original dropdown method for finding an enrollment center doesn't work. Instead I had to inspect headers in Chrome dev console.

[apendleton]

@EnviousElitist cool. I should have a chance tonight to update my branch and submit a PR, but if you want to do that sooner, go for it.