FIX MultiProc deadlock

[ccraddock]

FIX MultiProc deadlock

Reduced the complexity of the MultiProc processing to reduce likelihood for deadlock by:

removing semaphores and replacing with event, this allows for a timeout in the wait that safeguards against deadlock
setting results directly from apply_async callback rather than two stage processing, where a signal is sent from the callback, that wakes the multiproc.run() thread, which then sets the results -- this is where i think the previous deadlock was happening
Found deadlock where events would be cleared before they were handled, creating scenarios where thread waits for a signal that will never come -- fixed by changing the location from before the wait to after

Added missing close thread pool

Re-enabled multiproc tests

-- rebased with master

[codecov-io]

Current coverage is 71.12% (diff: 97.14%)

Merging #1756 into master will increase coverage by 0.04%

@@             master      #1756   diff @@
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+ Hits          36004      36037    +33   
+ Misses        13518      13501    -17   
  Partials       1127       1127          

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