When --direct is used when migrating a domain running on a hypervisor
that does not support direct migration (such as QEMU), the caller would
get the following error message:
this function is not supported by the connection driver:
virDomainMigrateToURI2
which is a complete nonsense since qemu driver implements
virDomainMigrateToURI2. This patch would emit a more sensible error in
this case:
Requested operation is not valid: direct migration is not supported
by the connection driver