Check initrd size on ppc64 and warn (#1060691)

ppc64 initrd cannot be larger than 32MiB, so log a warning if it is too
large.

Related: rhbz#1060691

src/pylorax/treebuilder.py

@@ -214,6 +214,13 @@ class TreeBuilder(object):
                 os.rename(initrd, initrd + backup)
             cmd = dracut + [outfile, kernel.version]
             runcmd(cmd, root=self.vars.inroot)
+
+            # ppc64 cannot boot images > 32MiB, check size and warn
+            if self.vars.arch.basearch == "ppc64" and os.path.exists(outfile):
+                st = os.stat(outfile)
+                if st.st_size > 32 * 1024 * 1024:
+                    logging.warning("ppc64 initrd %s is > 32MiB", outfile)
+
         os.unlink(joinpaths(self.vars.inroot,"/proc/modules"))
 
     def build(self):