tests: Fix tests/urchin/gossip.cc
tests: Fix tests/urchin/gossip.cc

After commit 67f4b55b16 "gms/gossiper: Fix is_gossip_only_member() logic",
storage_service is needed by gossip.

To fix, start storage_service in the test. Also, improve the
indentation.

duarten/scylla,gwicke/scylla,respu/scylla,victorbriz/scylla,linearregression/scylla,rluta/scylla,senseb/scylla,glommer/scylla,dwdm/scylla,eklitzke/scylla,rentongzhang/scylla,aruanruan/scylla,justintung/scylla,kangkot/scylla,guiquanz/scylla,raphaelsc/scylla,capturePointer/scylla,stamhe/scylla,kjniemi/scylla,rentongzhang/scylla,bowlofstew/scylla,senseb/scylla,acbellini/scylla,capturePointer/scylla,dwdm/scylla,avikivity/scylla,phonkee/scylla,kangkot/scylla,gwicke/scylla,duarten/scylla,capturePointer/scylla,justintung/scylla,bowlofstew/scylla,gwicke/scylla,wildinto/scylla,shaunstanislaus/scylla,duarten/scylla,raphaelsc/scylla,shaunstanislaus/scylla,phonkee/scylla,rluta/scylla,glommer/scylla,tempbottle/scylla,scylladb/scylla,tempbottle/scylla,linearregression/scylla,guiquanz/scylla,dwdm/scylla,linearregression/scylla,rentongzhang/scylla,tempbottle/scylla,phonkee/scylla,rluta/scylla,kangkot/scylla,victorbriz/scylla,aruanruan/scylla,scylladb/scylla,respu/scylla,stamhe/scylla,kjniemi/scylla,stamhe/scylla,bowlofstew/scylla,respu/scylla,victorbriz/scylla,asias/scylla,avikivity/scylla,scylladb/scylla,wildinto/scylla,guiquanz/scylla,asias/scylla,shaunstanislaus/scylla,scylladb/scylla,aruanruan/scylla,kjniemi/scylla,eklitzke/scylla,senseb/scylla,acbellini/scylla,eklitzke/scylla,acbellini/scylla,asias/scylla,glommer/scylla,raphaelsc/scylla,justintung/scylla,wildinto/scylla,avikivity/scylla