Replace CreateBucket with CreateBucketIfNotExists

[ahrtr]

Fix #17245

etcd creates the meta bucket twice on startup,

• etcd/server/etcdserver/bootstrap.go

  Line 212 in 4bc55e5

  schema.CreateMetaBucket(be.BatchTx())

• etcd/server/storage/mvcc/kvstore.go

  Line 118 in 4bc55e5

  schema.UnsafeCreateMetaBucket(tx)

Overall, it isn't a big problem. But let's replace CreateBucket with CreateBucketIfNotExists to remove the error message, to avoid any confusion.

[jmhbnz]

LGTM - Thanks @ahrtr

[serathius]

There is one optional followup. Etcd should not write error logs during normal function. We could add a e2e test that confirms that.

[ahrtr]

There is one optional followup. Etcd should not write error logs during normal function. We could add a e2e test that confirms that.

Agreed that it's nice to have.