Fix unit testing for several tests and do better error checking.

Fix unit testing for several tests and do better error checking.

* semantic/lex-spp-utests.el (semantic-lex-spp-write-utest):
* tests/cedet-utests.el (cedet-utest-eieio-classloader): Throw
  error if we cannot locate test files.

* semantic/utest-c.el (semantic-utest-c-compare)
  (semantic-utest-c-conditionals):
* semantic/lex-spp-utest.el (semantic-lex-spp-write-utest): Adapt
  to new directory structure and do better error checking to avoid
  silent failures in the future.