When killing QEMU, we defaulted to either killall or find the first
qemu process. This intefered with parallel builds, as we might kill
some other build's qemu process.
This makes QEMU write a pidfile in the local outdir directory and kill
only that when done.
Change-Id: I498b1e0833fcda9a7bd50111616dfba015e566bd
Signed-off-by: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>