Support building ethereal masterdirs

Dockerfile

@@ -1,30 +1,31 @@
 # 1) use alpine to generate a void environment
 FROM alpine:3.9 as stage0
-ARG REPOSITORY=https://alpha.de.repo.voidlinux.org/current
+ARG REPOSITORY=https://alpha.de.repo.voidlinux.org
 ARG ARCH=x86_64
 COPY keys/* /target/var/db/xbps/keys/
 RUN apk add ca-certificates && \
-  wget -O - https://alpha.de.repo.voidlinux.org/static/xbps-static-latest.$(uname -m)-musl.tar.xz | \
+  wget -O - ${REPOSITORY}/static/xbps-static-latest.$(uname -m)-musl.tar.xz | \
     tar Jx && \
   XBPS_ARCH=${ARCH} xbps-install.static -yMU \
-    --repository=${REPOSITORY} \
-    --repository=${REPOSITORY}/musl \
+    --repository=${REPOSITORY}/current \
+    --repository=${REPOSITORY}/current/musl \
     -r /target \
     base-minimal
 
 # 2) using void to generate the final build
 FROM scratch as stage1
-ARG REPOSITORY=https://alpha.de.repo.voidlinux.org/current
+ARG REPOSITORY=https://alpha.de.repo.voidlinux.org
 ARG ARCH=x86_64
+ARG BASEPKG=base-minimal
 COPY --from=stage0 /target /
 COPY keys/* /target/var/db/xbps/keys/
 RUN xbps-reconfigure -a && \
   mkdir -p /target/var/cache && ln -s /var/cache/xbps /target/var/cache/xbps && \
   XBPS_ARCH=${ARCH} xbps-install -yMU \
-    --repository=${REPOSITORY} \
-    --repository=${REPOSITORY}/musl \
+    --repository=${REPOSITORY}/current \
+    --repository=${REPOSITORY}/current/musl \
     -r /target \
-    base-minimal
+    ${BASEPKG}
 
 # 3) configure and clean up the final image
 FROM scratch