adbd's children should have SIGPIPE set to SIG_DFL.

POSIX lets you choose whether or not SIGPIPE disposition is inherited,
and Linux chose "yes". Work around that.

Bug: http://b/35209888
Test: "ps -A | head" without the toybox workaround
Change-Id: I6b5afa3d87eb2af04b24c6c37fa338ab60ad2336