Make the forking tests more reliable.  During copy the read(2) system call may fail with EAGAIN as the other forked process has already read the data.
Make the forking tests more reliable.  During copy the read(2)
system call may fail with EAGAIN as the other forked process has
already read the data.

bluhm/sosplice-regress,bluhm/sosplice-regress,bluhm/sosplice-regress