Ask QEMU to store the QEMU process PID in a file, this way we don't
have to parse running processes and analyze descendents.
This is done via QEMU command line argument "-pidfile".
[YOCTO #12001]
(From OE-Core rev: 67612dcd2a8a1aa1d683dddb0bd2f592886ff020)
Signed-off-by: Juro Bystricky <juro.bystricky@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>