Neither the VNC or SPICE code for password changes provides error
reporting at source, leading the callers to report a largely useless
generic error message.
Fixing this removes one of the two remaining needs for the undesirable
error_printf_unless_qmp() method.
While fixing this the error message hint is improved to recommend the
'password-secret' option which allows securely passing a password at
startup.
Reported-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
912f969e35