TF: build from tag

Build TF inside container from the tag specified in the Dockerfile.
This way we can easily fast forward to yet unreleased master/tags,
which contain fixes/new features we need. Once these are released
as proper version, we can change the tag from commit to the version
number. TF uses v0.6.15 scheme.

The tag in this commit is for 0.6.15-dev version. Reflect this in
tests.

terraform/Dockerfile

@@ -1,8 +1,7 @@
-FROM alpine:3.3
+FROM golang:1.6-alpine
 
 ENV PATH $PATH:/usr/local/bin
-ENV TERRAFORM_VER 0.6.13
-ENV TERRAFORM_ZIP terraform_${TERRAFORM_VER}_linux_amd64.zip
+ENV TERRAFORM_TAG 9cb08cb229a821753bdba8a6fc8c010767dea6c1
 ENV BINARY_WHITELIST \
   terraform \
   terraform-provider-aws \
@@ -14,8 +13,16 @@ ENV BINARY_WHITELIST \
   terraform-provisioner-local-exec \
   terraform-provisioner-remote-exec
 
-RUN apk add --update openssl openssh-client ca-certificates && rm -rf /var/cache/apk/*
+ENV PACKAGES "openssl openssh-client ca-certificates make bash git"
+
 RUN set -ex \
-       && wget https://releases.hashicorp.com/terraform/${TERRAFORM_VER}/${TERRAFORM_ZIP} -O /tmp/${TERRAFORM_ZIP} \
-       && unzip /tmp/${TERRAFORM_ZIP} -d /usr/local/bin ${BINARY_WHITELIST} \
-       && rm /tmp/${TERRAFORM_ZIP}
+    && apk add --update $PACKAGES \
+    && mkdir -p /go/src/github.com/hashicorp/ \
+    && cd /go/src/github.com/hashicorp/ \
+    && git clone https://github.com/hashicorp/terraform.git \
+    && cd terraform \
+    && git checkout $TERRAFORM_TAG \
+    && make dev \
+    && for file in $BINARY_WHITELIST ; do mv bin/$file /usr/local/bin ; done \
+    && rm -rf /go \
+    && rm -rf /var/cache/apk/*

terraform/terraform_spec.rb

@@ -38,7 +38,7 @@
   it "has the expected Terraform version" do
     expect(
       command("terraform version").stdout
-    ).to include("Terraform v0.6.13")
+    ).to include("Terraform v0.6.15-dev")
   end
 
   it "installs SSH" do