core: add distributed::invoke_on() variants not requiring a pointer to member
core: add distributed::invoke_on() variants not requiring a pointer to member

Current variants of distributed<T>::invoke_on() require member function to
invoke, which may be tedious to implement for some cases.  Add a variant
that supports invoking a functor, accepting the local instance by reference.

tempbottle/seastar,bzero/seastar,victorbriz/scylla,jonathanleang/seastar,phonkee/scylla,kjniemi/scylla,bzero/seastar,respu/scylla,kangkot/scylla,guiquanz/scylla,capturePointer/scylla,senseb/scylla,bowlofstew/seastar,glommer/scylla,kjniemi/scylla,leejir/seastar,phonkee/scylla,joerg84/seastar,slivne/seastar,flashbuckets/seastar,mixja/seastar,slivne/seastar,kjniemi/seastar,slivne/seastar,stamhe/seastar,linearregression/scylla,eklitzke/scylla,jonathanleang/seastar,cloudius-systems/seastar,phonkee/scylla,aruanruan/scylla,justintung/scylla,acbellini/scylla,wildinto/seastar,shaunstanislaus/scylla,rluta/scylla,kjniemi/seastar,wildinto/seastar,raphaelsc/scylla,capturePointer/scylla,hongliangzhao/seastar,printedheart/seastar,glommer/scylla,ducthangho/imdb,asias/scylla,norcimo5/seastar,avikivity/seastar,bowlofstew/seastar,rentongzhang/scylla,bowlofstew/scylla,dwdm/seastar,chunshengster/seastar,norcimo5/seastar,anzihenry/seastar,mixja/seastar,norcimo5/seastar,rluta/scylla,aruanruan/scylla,hongliangzhao/seastar,tempbottle/scylla,kjniemi/seastar,leejir/seastar,asias/scylla,jonathanleang/seastar,linearregression/scylla,scylladb/scylla-seastar,shaunstanislaus/scylla,avikivity/scylla,scylladb/seastar,linearregression/seastar,chunshengster/seastar,ducthangho/imdb,raphaelsc/seastar,duarten/scylla,gwicke/scylla,scylladb/scylla,dwdm/scylla,bzero/seastar,avikivity/scylla,stamhe/scylla,scylladb/seastar,stamhe/scylla,sjperkins/seastar,koolhazz/seastar,xtao/seastar,shyamalschandra/seastar,respu/scylla,acbellini/seastar,stamhe/seastar,dwdm/scylla,bowlofstew/seastar,leejir/seastar,scylladb/scylla,rentongzhang/scylla,shyamalschandra/seastar,printedheart/seastar,justintung/scylla,stamhe/scylla,sjperkins/seastar,cloudius-systems/seastar,mixja/seastar,xtao/seastar,bowlofstew/scylla,avikivity/scylla,avikivity/seastar,dreamsxin/seastar,scylladb/scylla,dwdm/seastar,acbellini/seastar,respu/scylla,linearregression/scylla,linearregression/seastar,dreamsxin/seastar,flashbuckets/seastar,sjperkins/seastar,raphaelsc/seastar,raphaelsc/scylla,guiquanz/scylla,flashbuckets/seastar,rentongzhang/scylla,asias/scylla,wildinto/seastar,cloudius-systems/seastar,tempbottle/scylla,joerg84/seastar,printedheart/seastar,scylladb/scylla-seastar,raphaelsc/scylla,xtao/seastar,tempbottle/seastar,syuu1228/seastar,wildinto/scylla,koolhazz/seastar,scylladb/seastar,eklitzke/scylla,capturePointer/scylla,koolhazz/seastar,wildinto/scylla,raphaelsc/seastar,glommer/scylla,victorbriz/scylla,rluta/scylla,stamhe/seastar,guiquanz/scylla,hongliangzhao/seastar,chunshengster/seastar,bowlofstew/scylla,tempbottle/seastar,linearregression/seastar,wildinto/scylla,victorbriz/scylla,syuu1228/seastar,dreamsxin/seastar,avikivity/seastar,dwdm/seastar,senseb/scylla,eklitzke/scylla,tempbottle/scylla,ducthangho/imdb,acbellini/scylla,scylladb/scylla-seastar,kangkot/scylla,senseb/scylla,gwicke/scylla,syuu1228/seastar,acbellini/seastar,justintung/scylla,dwdm/scylla,shaunstanislaus/scylla,kangkot/scylla,duarten/scylla,shyamalschandra/seastar,anzihenry/seastar,anzihenry/seastar,duarten/scylla,aruanruan/scylla,acbellini/scylla,gwicke/scylla,kjniemi/scylla,scylladb/scylla,joerg84/seastar