Reduced loadgenerator's image size (#52)

Reduce loadgenerator's image size from ~972MB to ~117MB

* Changed loadgen.sh to execute with `/bin/sh` as opposed to `/bin/bash`
* Changed dockerfile to a multi stage build
* Changed base image to `python:3-alpine` as opposed to `python:3.6`

src/loadgenerator/Dockerfile

@@ -1,7 +1,21 @@
-FROM python:3.6
+FROM python:3-alpine as base
+
+FROM base as builder
+
+RUN apk add --update --no-cache \
+    gcc \
+    linux-headers \
+    make \
+    musl-dev \
+    python-dev \
+    g++
 
 COPY requirements.txt .
-RUN pip install -r requirements.txt
+
+RUN pip install --install-option="--prefix=/install" -r requirements.txt
+
+FROM base
+COPY --from=builder /install /usr/local
 
 COPY . .
 ENTRYPOINT ./loadgen.sh

src/loadgenerator/loadgen.sh

@@ -1,4 +1,4 @@
-#!/bin/bash -eu
+#!/bin/sh -eu
 #
 # Copyright 2018 Google LLC
 #