Return a 404 on ResourceNotFoundException

Current implementation returns a 500, which is incorrect.
A ResourceNotFoundException indicates a resource could not
be found, which is REST translates to a 404 http code.

Returning a 404 will ensure that clients will be able
to correctly identify missing projects.

Bug: Issue 16730
Change-Id: Ifb331dcee7165b7b2f2b33879c6c3cd2edfe8cc2
2 files changed