Reduces the number of connections to mongo created

[flovilmart]

Reduces the number of times we create a new ParseServer in the tests so we don't spawn 1k+ connections.

@gfosco related to the mongo problems we faced when running locally.

[codecov-io]

Current coverage is 91.92%

Merging #1111 into master will not affect coverage as of 3182fc1

@@            master   #1111   diff @@
======================================
  Files           91      91       
  Stmts         5736    5736       
  Branches      1043    1043       
  Methods          0       0       
======================================
  Hit           5273    5273       
  Partial         11      11       
  Missed         452     452       

Review entire Coverage Diff as of 3182fc1

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