#79 close django db connection before fork

[Koed00]

The sentinel saves a statistic to the cache provider just before forking the workers. If this cache provider is a database backend, the connection stays open and gets forked and it crashes. Solution is to close any db connection before forking.

[codecov-io]

Current coverage is 95.83%

Merging #80 into master will not affect coverage as of 9f575c4

@@            master     #80   diff @@
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  Files           37      37       
  Stmts         2160    2161     +1
  Branches         0       0       
  Methods          0       0       
======================================
+ Hit           2070    2071     +1
  Partial          0       0       
  Missed          90      90       

Review entire Coverage Diff as of 9f575c4

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