qemu.bbclass: return qemuwrapper instead of qemu-allarch

qemu.bbclass: return qemuwrapper instead of qemu-allarch

When qemu bbclass is inherited from a recipe that is not architecture
dependent, qemu_run_binary will return "qemu-allarch". However this
binary does not exist. Instead, return "qemuwrapper" which will, in
turn, execute the right binary for the target the image was built for.

[YOCTO #2599]

(From OE-Core rev: 149a564bba7d3e1c2054ae6d908835ebd95b9084)

Signed-off-by: Laurentiu Palcu <laurentiu.palcu@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>