system keyspace: implement get_bootstrap_state
system keyspace: implement get_bootstrap_state

To avoid spreading the futures all over, we will resort to a cache with this,
the same way we did for the dc/rack information.

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

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