feat(rootfs/Dockerfile): add shfmt shell formatter (#170)

Author: mboersma

README.md

@@ -32,6 +32,7 @@ creating [issues][] and submitting [pull requests][].
 * [Packer][]: build automated machine images
 * [ruby][]: ruby scripting language
 * [shellcheck][]: static analysis for shell scripts
+* [shfmt][]: shell script parser, formatter, and interpreter
 * [shyaml][]: YAML access from the command line
 * [test-cover.sh][]: test coverage for multiple Go packages
 * [unzip][]: list, test, and extract files from ZIP archives
@@ -91,11 +92,12 @@ The latest deis/go-dev Docker image is available at:
 [Packer]: https://github.com/hashicorp/packer
 [ruby]: https://www.ruby-lang.org/
 [shellcheck]: https://github.com/koalaman/shellcheck
+[shfmt]: https://github.com/mvdan/sh
 [shyaml]: https://github.com/0k/shyaml
 [test-cover.sh]: https://github.com/deis/docker-go-dev/tree/master/rootfs/usr/local/bin/test-cover.sh
 [Ubuntu 16.04]: https://hub.docker.com/_/ubuntu/
 [unzip]: https://linux.die.net/man/1/unzip
 [upx]: http://upx.sourceforge.net/
 [vim]: http://www.vim.org/
 [ruby]: https://www.ruby-lang.org/
-[wamerican]: https://packages.ubuntu.com/xenial/wamerican
+[wamerican]: https://packages.ubuntu.com/xenial/wamerican

rootfs/Dockerfile

@@ -13,6 +13,7 @@ ENV AZCLI_VERSION=2.0.63 \
     GOLANGCI_LINT_VERSION=v1.16.0 \
     PROTOBUF_VERSION=3.7.0 \
     SHELLCHECK_VERSION=v0.6.0 \
+    SHFMT_VERSION=2.6.4 \
     PATH=$PATH:/usr/local/go/bin:/go/bin:/usr/local/bin/docker \
     GOPATH=/go
 
@@ -96,6 +97,9 @@ RUN \
   && curl -sfL https://install.goreleaser.com/github.com/golangci/golangci-lint.sh | sh -s -- -b ${GOPATH}/bin ${GOLANGCI_LINT_VERSION} \
   && curl -o /usr/local/bin/shellcheck -sSL https://shellcheck.storage.googleapis.com/shellcheck-${SHELLCHECK_VERSION}.linux-x86_64 \
   && chmod +x /usr/local/bin/shellcheck \
+  && go get -u mvdan.cc/sh/cmd/shfmt \
+  && git -C "$GOPATH/src/mvdan.cc/sh" checkout -q "v$SHFMT_VERSION" \
+  && go install -a -ldflags '-extldflags "-static"' mvdan.cc/sh/cmd/shfmt \
   && pip install --disable-pip-version-check --no-cache-dir azure-cli==${AZCLI_VERSION} shyaml \
   && apt-get purge --auto-remove -y libffi-dev python-dev python-pip \
   && apt-get autoremove -y \