Disable plymouth for PowerPC release >f27

as bypass for pending bug
https://bugzilla.redhat.com/show_bug.cgi?id=1571860

Signed-off-by: Michel Normand <normand@linux.vnet.ibm.com>

createhdds.py

@@ -297,6 +297,9 @@ class VirtInstallImage(object):
                 args.extend(("--graphics", "none", "--extra-args", "console=ttyS0"))
             else:
                 args.extend(("--graphics", "vnc", "--noautoconsole"))
+            if arch in ['ppc64','ppc64le'] and (str(self.release).lower() == 'rawhide' or int(self.release) > 27):
+                logger.info("disable plymouth as bypass bug#1571860")
+                args.extend(("--extra-args", "plymouth.enable=0"))
             # this is a hacky workaround for a weird bug on Fedora's prod
             # openQA server:
             # https://bugzilla.redhat.com/show_bug.cgi?id=1387798