Changing a host architecture or a CPU is not as easy as assigning a new
value to the appropriate element in virCaps since there is a relation
between the CPU and host architecture (we don't really want to test
anything on an AArch64 host with core2duo CPU). This patch introduces
qemuTestSetHostArch and qemuTestSetHostCPU helpers which will make sure
the host architecture matches the host CPU.
Signed-off-by: NJiri Denemark <jdenemar@redhat.com>