utils/wa_results_collector: nicely complain for not valid filter
utils/wa_results_collector: nicely complain for not valid filter

Let's warn the used when filters are not valid, instead of raising an
confusing KeyError exception.

Signed-off-by: Patrick Bellasi <431c86f368affbc3148c4669fbd465131f7e82cb@arm.com>

bjackman/lisa,ARM-software/lisa,credp/lisa,credp/lisa,credp/lisa,bjackman/lisa,ARM-software/lisa,ARM-software/lisa,ARM-software/lisa,credp/lisa