testQEMUSchemaValidate(Command): Allow skipping validation of deprecated fields

testQEMUSchemaValidate(Command): Allow skipping validation of deprecated fields

Some test cases are used to validate interactions with old qemu. We need
to skip validation of deprecation with those once it will be added.

In case of commands which were already replaced by code based on
capabilities we can skip the full validation once the command is
removed.

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