Use from_service_account_info instead of from_json_keyfile_dict for google credentials

[mbertrand]

Pre-Flight checklist

• [ ] Testing
  • [ ] Code is tested
  • [ ] Changes have been manually tested

What are the relevant tickets?

Closes #1007

What's this PR do?

Switches from ServiceAccountCredentials.from_json_keyfile_dict (no longer supported) to ServiceAccountCredentials.from_service_account_info

How should this be manually tested?

• Ask me for the GA_* settings
• Change the UUID for one of your videos to 3c142cf25d1a4933be574d2695e34338
• While logged in as someone allowed to view that video, go to http://localhost:8089/api/v0/videos/3c142cf25d1a4933be574d2695e34338/analytics/ and you should get JSON back, not a 500 error

[codecov-commenter]

Codecov Report

Merging #1008 (798dcf3) into master (f8e3d0d) will increase coverage by 1.41%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1008      +/-   ##
==========================================
+ Coverage   96.03%   97.44%   +1.41%     
==========================================
  Files         182      131      -51     
  Lines        7345     4781    -2564     
  Branches      251        0     -251     
==========================================
- Hits         7054     4659    -2395     
+ Misses        257      122     -135     
+ Partials       34        0      -34     

Impacted Files	Coverage Δ
ui/utils.py
ui/constants.py
ui/exceptions.py
odl_video/celery.py
cloudsync/utils.py
cloudsync/views.py
odl_video/settings.py
mail/tasks.py
odl_video/models.py
odl_video/constants.py
... and 41 more

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