Container parse logic cannot handle NORMAL (default) case
currently. So, if -t option is not used while generating a
Container, unsupported image type is reported during runtime.
Change the default type to CLASSIC, and end-user can use
-t option to switch to MULTIBOOT if needed.
Signed-off-by: Sai Talamudupula <sai.kiran.talamudupula@intel.com>