futures_test: silence exceptional future ignored messages
futures_test: silence exceptional future ignored messages

Some of the tests won't do the final catch, leading to warning messages that,
specially coming from a test, can be quite confusing. Silence them

Signed-off-by: Glauber Costa <f8b79557d19b40666ebe336545a0b6178af65685@cloudius-systems.com>

dwdm/seastar,syuu1228/seastar,jonathanleang/seastar,syuu1228/seastar,bowlofstew/seastar,scylladb/seastar,stamhe/seastar,flashbuckets/seastar,leejir/seastar,cloudius-systems/seastar,chunshengster/seastar,kjniemi/seastar,leejir/seastar,printedheart/seastar,xtao/seastar,bowlofstew/seastar,linearregression/seastar,cloudius-systems/seastar,bowlofstew/seastar,avikivity/seastar,norcimo5/seastar,shyamalschandra/seastar,scylladb/scylla-seastar,scylladb/seastar,acbellini/seastar,tempbottle/seastar,xtao/seastar,chunshengster/seastar,linearregression/seastar,scylladb/scylla-seastar,sjperkins/seastar,joerg84/seastar,wildinto/seastar,sjperkins/seastar,dwdm/seastar,kjniemi/seastar,kjniemi/seastar,koolhazz/seastar,norcimo5/seastar,hongliangzhao/seastar,syuu1228/seastar,avikivity/seastar,scylladb/seastar,shyamalschandra/seastar,anzihenry/seastar,koolhazz/seastar,joerg84/seastar,anzihenry/seastar,acbellini/seastar,scylladb/scylla-seastar,shyamalschandra/seastar,jonathanleang/seastar,jonathanleang/seastar,cloudius-systems/seastar,dreamsxin/seastar,dreamsxin/seastar,xtao/seastar,dreamsxin/seastar,flashbuckets/seastar,wildinto/seastar,printedheart/seastar,wildinto/seastar,hongliangzhao/seastar,dwdm/seastar,stamhe/seastar,sjperkins/seastar,koolhazz/seastar,linearregression/seastar,norcimo5/seastar,flashbuckets/seastar,tempbottle/seastar,joerg84/seastar,hongliangzhao/seastar,printedheart/seastar,acbellini/seastar,leejir/seastar,chunshengster/seastar,stamhe/seastar,avikivity/seastar,anzihenry/seastar,tempbottle/seastar