Always check for root disks unless MINIO_CI_CD is set (#14232)

The current code considers a pool with all root disks to be as part
of a testing environment even if there are other pools with mounted
disks. This will result to illegitimate writing in root disks.

Fix this by simplifing the logic: require MINIO_CI_CD in order to skip
root disk check.

docs/bucket/replication/setup_3site_replication.sh

@@ -25,6 +25,7 @@ catch() {
 catch
 
 set -e
+export MINIO_CI_CD=1
 export MINIO_BROWSER=off
 export MINIO_ROOT_USER="minio"
 export MINIO_ROOT_PASSWORD="minio123"