db: Move "Populating Keyspace ..." message from WARN to INFO level
db: Move "Populating Keyspace ..." message from WARN to INFO level

WARN level is for messages which should draw log reader's attention,
journalctl highlights them for example. Populating of keyspace is a
fairly normal thing, so it should be logged on lower level.

gwicke/scylla,raphaelsc/scylla,rentongzhang/scylla,victorbriz/scylla,kjniemi/scylla,glommer/scylla,capturePointer/scylla,capturePointer/scylla,raphaelsc/scylla,kjniemi/scylla,duarten/scylla,kjniemi/scylla,scylladb/scylla,avikivity/scylla,wildinto/scylla,gwicke/scylla,scylladb/scylla,aruanruan/scylla,justintung/scylla,rentongzhang/scylla,linearregression/scylla,scylladb/scylla,aruanruan/scylla,aruanruan/scylla,kangkot/scylla,duarten/scylla,gwicke/scylla,linearregression/scylla,respu/scylla,phonkee/scylla,wildinto/scylla,raphaelsc/scylla,rentongzhang/scylla,kangkot/scylla,shaunstanislaus/scylla,shaunstanislaus/scylla,justintung/scylla,phonkee/scylla,asias/scylla,respu/scylla,avikivity/scylla,respu/scylla,scylladb/scylla,avikivity/scylla,senseb/scylla,asias/scylla,kangkot/scylla,victorbriz/scylla,glommer/scylla,wildinto/scylla,victorbriz/scylla,glommer/scylla,capturePointer/scylla,senseb/scylla,justintung/scylla,duarten/scylla,shaunstanislaus/scylla,senseb/scylla,asias/scylla,linearregression/scylla,phonkee/scylla