Introduce the --require-full-coverage in analyze_outcomes.py so that
when analyze_outcomes.py --require-full-coverage is called, those
tests that are not executed and are not in the allowed list issue an
error instead of a warning.
Note that it is useful to run analyze_outcomes.py on incomplete test
results, so this error mode needs to remain optional in the long
term.
Signed-off-by: Tomás González <tomasagustin.gonzalezorlando@arm.com>