S3 gateway signature probe use a unique bucket (#6190)
S3 gateway signature probe use a unique bucket (#6190)

This fixes an issue because someone is
using `probe-bucket-sign` bucket name in
region 'eu-central-1'
NitishT/minio,jimjag/minio,aead/minio,NitishT/minio,aead/minio,aead/minio,minio/minio,aead/minio,NitishT/minio,donatello/minio,fwessels/minio,jimjag/minio,donatello/minio,krishnasrinivas/minio,fwessels/minio,fwessels/minio,krisis/minio,aead/minio,harshavardhana/minio,harshavardhana/minio,krishnasrinivas/minio,fwessels/minio,aead/minio,balamurugana/minio,NitishT/minio,harshavardhana/minio,krisis/minio,harshavardhana/minio,harshavardhana/minio,vadmeste/minio,minio/minio,harshavardhana/minio,aead/minio,vadmeste/minio,krishnasrinivas/minio,harshavardhana/minio,aead/minio,jimjag/minio,krishnasrinivas/minio,balamurugana/minio,jimjag/minio,harshavardhana/minio