file_contexts: don't delete intermediate on failure

Currently, if an error is detected in a file_contexts
file, the intermediate file_context.tmp file is removed,
thus making debugging of build issues problematic.

Instead, employ checkfc tool during the compilation recipe
so the m4 concatenated intermediate is preserved on
failure.

Change-Id: Ic827385d3bc3434b6c2a9bba5313cd42b5f15599
Signed-off-by: William Roberts <william.c.roberts@intel.com>