bin/ebuild-ipc.py: nonblocking fifo write

Use nonblocking write instead of a fork for writing to the fifo.
This has the advantage of avoiding a possible python futex deadlock
following fork as reported in bug #524328.

X-Gentoo-Bug: 524328
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=524328