The 'arch' property gives a hint on which architecture the guest image runs.

This can be use to select the correct QEMU binary path.
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20181013004034.6968-6-f4bug@amsat.org>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Signed-off-by: NFam Zheng <famz@redhat.com>