memcached: optimize handle_get()
memcached: optimize handle_get()

We don't really need to copy keys as the parser is not reused until
we're done.

Also, in case of a single key we don't use map_reduce() which
saves us one allocation (reducer).

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