dockerfile: Make builder image configurable
# Prepare and build gadget artifacts in a container
+ARG BUILDER_IMAGE=ubuntu:20.04
+
# BCC built from the gadget branch in the kinvolk/bcc fork.
# See BCC section in docs/CONTRIBUTING.md for further details.
ARG BCC="quay.io/kinvolk/bcc:64a64b4ba0a719fb6b79a4705f29ad5e1fa1e47d-focal-release"
-ARG OS_TAG=20.04
FROM ${BCC} as bcc
-FROM ubuntu:${OS_TAG} as builder
+FROM ${BUILDER_IMAGE} as builder
ARG ENABLE_BTFGEN=false
ENV ENABLE_BTFGEN=${ENABLE_BTFGEN}
