Fix Parse.Push flaky tests

[dplewis]

New Pull Request Checklist

• I am not disclosing a vulnerability.
• I am creating this PR in reference to an issue.

Issue Description

There are flaky tests in Parse.Push.spec.js and PushController.spec.js.

• PushController properly creates _PushStatus
• PushController should not enqueue push when device token is not set
• Parse.Push does not get stuck with _PushStatus 'running' on 1 installation added
• Parse.Push does not get stuck with _PushStatus 'running' on 1 installation removed
• Many others

Related issue: FILL_THIS_OUT

Approach

• Ensure a sent push is completed before continuing
• Remove setTimeout
• Use async/await
• Utilize new Parse.Push.getPushStatus

TODOs before merging

• Add test cases
• Add entry to changelog
• Add changes to documentation (guides, repository pages, in-code descriptions)
• Add security check
• Add new Parse Error codes to Parse JS SDK
• ...

[codecov]

Codecov Report

Merging #7263 (51ca146) into master (687f4b7) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7263      +/-   ##
==========================================
+ Coverage   94.03%   94.04%   +0.01%     
==========================================
  Files         179      179              
  Lines       13137    13137              
==========================================
+ Hits        12353    12355       +2     
+ Misses        784      782       -2     

Impacted Files	Coverage Δ
src/Adapters/Files/GridFSBucketAdapter.js	80.32% <0.00%> (+0.81%)	⬆️
src/ParseServerRESTController.js	98.50% <0.00%> (+1.49%)	⬆️

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[davimacedo]

LGTM!

[parseplatformorg]

🎉 This change has been released in version 5.0.0-beta.1

[parseplatformorg]

🎉 This change has been released in version 5.0.0