Reduced cartservice Docker Image size (#46)

Reduces docker image size for cartservice from ~2.36 GB to ~157 MB
Fixes Issue #36 

![image-size](https://user-images.githubusercontent.com/7820716/45908973-37a31e00-bdb4-11e8-92d3-d84acfb1c10f.png)

src/cartservice/Dockerfile

@@ -1,22 +1,35 @@
-# cartservice_probe
-FROM golang:1.10 as builder
+FROM golang:1.10 as probe
 RUN wget -qO/go/bin/dep https://github.com/golang/dep/releases/download/v0.5.0/dep-linux-amd64 && \
-      chmod +x /go/bin/dep
+    chmod +x /go/bin/dep
 ENV PROJECT github.com/GoogleCloudPlatform/microservices-demo/src/cartservice/probe
 WORKDIR /go/src/$PROJECT
 COPY probe/Gopkg.* ./
 RUN dep ensure --vendor-only -v
 COPY ./probe ./
 RUN go build -o /cartservice_probe .
 
-# cartservice
-FROM gcr.io/google-appengine/aspnetcore:2.1.0
-COPY --from=builder /cartservice_probe /cartservice_probe
-RUN apt-get update && apt-get install net-tools telnet
+FROM microsoft/dotnet:2.1-sdk-alpine as builder
 WORKDIR /app
 COPY . .
 RUN dotnet restore && \
     dotnet build && \
-    dotnet publish
-WORKDIR /app/bin/Debug/netcoreapp2.0
-ENTRYPOINT ["dotnet", "cartservice.dll", "start"]
+    dotnet publish -c release -r linux-musl-x64 -o /cartservice
+
+# cartservice
+FROM alpine:3.8
+# Add the probe
+COPY --from=probe /cartservice_probe /cartservice_probe
+# Dependencies for runtime
+# busybox-extras => telnet
+RUN apk add --no-cache \
+    busybox-extras \
+    libc6-compat \
+    libunwind \
+    libuuid \
+    libgcc \
+    libstdc++ \
+    libintl \
+    icu
+WORKDIR /app
+COPY --from=builder /cartservice .
+ENTRYPOINT ["./cartservice", "start"]

src/cartservice/cartservice.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp2.0</TargetFramework>
+    <TargetFramework>netcoreapp2.1</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>