Parallels: remove disk serial number check

OpenStack needs disk serial number setup because
nova boot --block-device-mapping command generates that param in
libvirt xml. I took QEMU libvirt driver behavior as a base.
QEMU driver skips inability to set serial and continues work.
So Parallels driver will ignore this param too and let domain
boot.

src/parallels/parallels_sdk.c

@@ -2437,10 +2437,8 @@ static int prlsdkCheckDiskUnsupportedParams(virDomainDiskDefPtr disk)
     }
 
     if (disk->serial) {
-        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
-                       _("Setting disk serial number is not "
+        VIR_INFO("%s", _("Setting disk serial number is not "
                          "supported by parallels driver."));
-        return -1;
     }
 
     if (disk->wwn) {