Fix FreeBSD VM on Travis not shutting down

[nurupo]

Proper fix for #1071.

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This change is 

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[iphydf]

Reviewable status: 0 of 1 approvals obtained

WIP

[codecov]

Codecov Report

Merging #1075 into master will decrease coverage by 0.1%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master   #1075     +/-   ##
========================================
- Coverage    82.6%   82.5%   -0.2%     
========================================
  Files          81      81             
  Lines       14437   14437             
========================================
- Hits        11935   11916     -19     
- Misses       2502    2521     +19

Impacted Files	Coverage Δ
toxcore/crypto_core_test.cc	90.3% <0%> (-9.7%)	⬇️
toxcore/friend_connection.c	93.6% <0%> (-2.1%)	⬇️
toxcore/net_crypto.c	93.1% <0%> (-0.5%)	⬇️
toxcore/onion_client.c	95% <0%> (-0.4%)	⬇️
toxcore/Messenger.c	85.7% <0%> (-0.3%)	⬇️
toxcore/LAN_discovery.c	84.9% <0%> (+0.9%)	⬆️

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[nurupo]

@iphydf should be fixed now. Travis-CI passes, Circle-CI tsan fails.

[iphydf]

Thanks, I don't know why coveralls is complaining.