Update instance_report.py scraper to match App Engine UI

Summary:
This fixes 3 issues:
1) There is a new field for the App Engine version.
2) During new version rollout there are 2 rows of instance summaries.
3) Instance summary data is no longer present on /instances, it is
   delay-loaded by the web UI by calling /instance_summary.

Test Plan:
I downloaded the instance summary HTML and ran it against the script in
"dry-run" and "verbose" mode:

  $ ./gae_dashboard_curl.py 'https://appengine.google.com/instance_summary?app_id=s~khan-academy' chris@khanacademy.org >instance_summary.html
  $ <instance_summary.html ./instance_report.py -vn 0

Reviewers: csilvers

Reviewed By: csilvers

Differential Revision: http://phabricator.khanacademy.org/D8018