=act 3571 quiet down exceptions from `Socket.shutdownOutput()`

Backport from this spray commit:

https://github.com/spray/spray/commit/e4068046a5a501b059e0cf9305a85f9c1aca7e42
(cherry picked from commit 972284ce715835f39dd00b038ef9add3354e4043)
Merge pull request #1801 from jrudolph/i/3571/fix-backport

=act 3571 quiet down exceptions from `Socket.shutdownOutput()`