Add rule for execute rescratch command only for flash in builder mode.

pym/cl_builder.py

@@ -320,6 +320,11 @@ class cl_builder(color_print):
         sourceDirectory = self.clVars.Get('cl_builder_path')
         bindDirectory = pathJoin(buildDirectory,
                         self.clVars.Get('cl_builder_squash_path'))
+        if not (self.clVars.Get('os_root_type') == 'livecd' \
+            and os.access(self.clVars.Get('cl_builder_iso_path'),os.W_OK)):
+            self.printERROR(
+                _("The computer must be load from the flash in Builder mode"))
+            return False
         self.printRescratchInfo()
         if not self.checkVariables(rescratch=True):
             return False