ch: Do not add stub console to ch VMs

ch: Do not add stub console to ch VMs

virDomainDefAddConsoleCompat in post parsing step appends a stub console
of type VIR_DOMAIN_CHR_TYPE_NULL to ch VMs' Domain XML. Cloud-hypervisor's
deviceValidateCallback (chValidateDomainDeviceDef) checks that the type of
stub console is not of type VIR_DOMAIN_CHR_TYPE_PTY and throws an error.

This commit introduces NO_STUB_CONSOLE feature check to Domain features and
uses it to skip adding stub console to ch VMs.

Signed-off-by: Praveen K Paladugu <prapal@linux.microsoft.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>