qemuxml2(argv|xml)test: Modernize 'sound-device' case

qemuxml2(argv|xml)test: Modernize 'sound-device' case

Drop the unnecessary disk definition and use x86_64 emulator.

For 'qemuxml2argvtest' replace the fake-caps invocation by a 4.2.0
version-locked invocation and  add a '_CAPS_LATEST' invocation.

For 'qemuxml2xmltest' convert to use '_CAPS_LATEST' only.

There are no sound-device relevant changes in the output files.

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