luminous unsupported rgw backend beast(by default)

[rikewang]

version: v2.3.1

ERR:

++/opt/ceph-container/bin/demo.sh:172: bootstrap_rgw(): RGW_FRONTEND_TYPE=beast
++/opt/ceph-container/bin/demo.sh:173: bootstrap_rgw(): log 'ERROR: unsupported rgw backend type beast for your Ceph release luminous, use at least the Mimic version.'
++/opt/ceph-container/bin/common_functions.sh:7: log(): '[' -z 'ERROR: unsupported rgw backend type beast for your Ceph release luminous, use at least the Mimic version.' ']'

scripts here explain it: /opt/ceph-container/bin/demo.sh

  if [[ "$RGW_FRONTEND_TYPE" == "beast" ]]; then
    if [[ "$CEPH_VERSION" == "luminous" ]]; then
      RGW_FRONTEND_TYPE=beast
      log "ERROR: unsupported rgw backend type $RGW_FRONTEND_TYPE for your Ceph release $CEPH_VERSION, use at least the Mimic version."
      exit 1
    fi
  fi

tips:
support envs args to set rgw backend freely, not just fixed envs.