Enable integration tests to be randomized

[dplewis]

Allowing the test suite to run in a random order will help find test passes only based on a previously ran test.

• Adds new Parse.Object.unregisterSubclass feature
• Properly closes test created servers
• Generate unique username and password for user tests
• Properly handle unsorted queries (results returned in random order)
• Improve tests with background operations
• Remove setTimeout when possible

[codecov]

Codecov Report

Merging #1317 (ebedc02) into master (724485d) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #1317   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           60        60           
  Lines         5847      5853    +6     
  Branches      1312      1313    +1     
=========================================
+ Hits          5847      5853    +6     

Impacted Files	Coverage Δ
src/ParseObject.js	100.00% <100.00%> (ø)

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[dplewis]

@davimacedo @mtrezza I ran the entire suite 20 times locally without any issues. This should be good to go.

[mtrezza]

LGTM! Nice, I expected more fails, let's see how Parse Server does randomized.

[dplewis]

I hope so there are 2800 test in the server repo.