Http Server: code generation improve error handling

This series changes the somehow cryptic code generation error messages
to more meaningful ones.

It catches all exception and print an error message with the current
file being parsed.

It also tries to identify if a missing attribute causes an error and
report the missing attribute with its whereabout.

Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>