Fix bug of installation from CD which booted as builder.

Reference http://www.calculate-linux.ru/boards/8/topics/4782.

pym/cl_fill_install.py

@@ -539,7 +539,7 @@ class fillVars(object, glob_attr):
 
     def get_cl_image_path(self):
         if self.Get('os_root_type') == "livecd":
-            if self.Get('os_scratch') == "on":
+            if self.Get('os_scratch') == "on" and path.exists('/mnt/flash'):
                 livedistr = ['/mnt/flash']
             elif path.exists('/mnt/squash'):
                 livedistr = ['/mnt/livecd']