Specify full golang version in Dockerfiles and build helper script (#227)

Addresses #222.

Plugins and the binaries loading them need to be built with the exact
same go version.

Also update README instructions.

environments/go/Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.8
+FROM golang:1.8.1
 
 ENV GOPATH /usr
 ENV APP	   ${GOPATH}/src/github.com/fission/fission/environments/go

environments/go/README.md

@@ -10,6 +10,13 @@ It's a Docker image containing a Go 1.8 runtime, along with a dynamic loader.
 docker build -t USER/go-runtime . && docker push USER/go-runtime
 ```
 
+Note that if you build the runtime, you must also build the go-builder
+image, to ensure that it's at the same version of go:
+
+```
+cd builder && docker build -t USER/go-builder . && docker push USER/go-builder
+```
+
 ## Using the image in fission
 
 You can add this customized image to fission with "fission env
@@ -28,7 +35,6 @@ fission env update --name go-runtime --image USER/go-runtime
 After this, fission functions that have the env parameter set to the
 same environment name as this command will use this environment.
 
-
 ## Creating functions to use this image
 
 See the [examples README](examples/go/README.md).

environments/go/builder/Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.8
+FROM golang:1.8.1
 
 ENV GOPATH /usr
 RUN go get github.com/fission/fission

environments/go/builder/go-function-build

@@ -8,4 +8,4 @@ else
     filename=$1
 fi
 
-docker run --rm -v $(pwd):/build -w /build fission/go-builder go build -buildmode=plugin -o function.so $filename && echo "Compiled plugin: function.so. Use 'fission function create' to upload to fission."
+docker run --rm -v $(pwd):/build -w /build fission/go-builder:1.8.1 go build -buildmode=plugin -o function.so $filename && echo "Compiled plugin: function.so. Use 'fission function create' to upload to fission."