ctf: better enum and variant verification

ctf: better enum and variant verification

Check if enums are valid integers
Check if variants are not using unspecified tags
Check for variant tags recursively
Check for out of range variants
Check for non-intersection between variant and tag

Change-Id: Idd6a98673d8bb3b0a7a1649893a2e21f230a1bcc
Signed-off-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/19410
Reviewed-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
IP-Clean: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Tested-by: Hudson CI