Docker: use 'golang:alpine' base & install mailcap for mime-type support

Update changelog to reflect this

Dockerfile.revad

@@ -36,7 +36,10 @@ RUN make build-revad-docker && \
 
 RUN mkdir -p /etc/revad/ && echo "" > /etc/revad/revad.toml
 
-FROM scratch
+FROM golang:alpine
+
+RUN apk --no-cache add \
+  mailcap
 
 EXPOSE 9999 10000
 

changelog/unreleased/set-cgo-enabled-0-flag.md

@@ -1,8 +1,13 @@
-Bugfix: Set CGO_ENABLED flag for 'scratch' based docker builds
+Bugfix: 'golang:alpine' as base image & CGO_ENABLED just for the CLI
+
+Some of the dependencies used by revad need CGO to be enabled in order to
+work. We also need to install the 'mime-types' in alpine to correctly
+detect them on the storage-providers.
 
 The CGO_ENABLED=0 flag was added to the docker build flags so that it will
 produce a static build. This allows usage of the 'scratch' image for
-reduction of the docker image size.
+reduction of the docker image size (e.g. the reva cli).
 
 https://github.com/cs3org/reva/issues/1765
-https://github.com/cs3org/reva/pull/1766
+https://github.com/cs3org/reva/pull/1766
+https://github.com/cs3org/reva/pull/1797