qemu: capabilities: Preserve location of the default machine type when stripping...

qemu: capabilities: Preserve location of the default machine type when stripping aliases for tests

Internally the preferred machine which is 'pc' for x86_64 must be kept
in the first place in the array of machines. This was not the case when
stripping the machine aliases for use in tests (so that test output
stays stable) where we've created a new entry for the alias. This means
that the original name (e.g. pc-i440fx-8.1) stayed in the first place.

To fix this we now swap the names around and create a new entry at the
end for the specific type. Additionally the default flag is not
propagated to the copy.

This is also visible now in the output of 'qemuxml2xmltest' as the test
cases which use the default machine type return to 'pc' instead of the
more specific name.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>