Clean up dapper dockerfile
Cleaned up environment var which aren't necessary and weren't working
properly anyhow as they relied on DAPPER_SOURCE which is defined in the
same line.
Resolves:
FROM quay.io/submariner/shipyard-dapper-base
-ENV DAPPER_ENV=REPO DAPPER_ENV=TAG \
- DAPPER_SOURCE=/go/src/github.com/submariner-io/submariner DAPPER_DOCKER_SOCKET=true \
- TRASH_CACHE=${DAPPER_SOURCE}/.trash-cache HOME=${DAPPER_SOURCE}
+ENV DAPPER_ENV="REPO TAG" \
+ DAPPER_SOURCE=/go/src/github.com/submariner-io/submariner DAPPER_DOCKER_SOCKET=true
ENV DAPPER_OUTPUT=${DAPPER_SOURCE}/output
WORKDIR ${DAPPER_SOURCE}
