Re: [Libvir] PATCH: Check for /usr/bin/qemu* binaries before starting guest

The attached patch fixes two issues - It explicitly checks to see if the requested /usr/bin/qemu* binary actually exists before fork()/exec()'ing it. While its technically possible to catch the execve() failure of ENOENT, its a real pain to feed this error back to the qemu daemon because we're in a sub-process at that point. The obvious & easy solution is to thus check to see if the binary exists before trying to fork. - It only passes the -no-kqemu flag if we're running matching arch to the host. Previously it would pass the -no-kqemu flag even if running an x86_64 guest on i686 platform - QEMU then exited with error because the -no-kqemu flag is not recognised on x86_64 when running on i686 host.