system keyspaces: use existing constant instead of hardcoding keyspace name
system keyspaces: use existing constant instead of hardcoding keyspace name

Signed-off-by: Glauber Costa <f8b79557d19b40666ebe336545a0b6178af65685@cloudius-systems.com>
Reviewed-by: Pekka Enberg <add4fcd06328a394f0ad91feda7ee057316dc5ed@cloudius-systems.com>

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