Add dotnetcore2.0 build image

dotnetcore2.0/build/Dockerfile

@@ -0,0 +1,20 @@
+FROM lambci/lambda-base:build
+
+ENV PATH=/var/lang/bin:/usr/local/bin:/usr/bin/:/bin \
+    LD_LIBRARY_PATH=/var/lang/lib:/lib64:/usr/lib64:/var/runtime:/var/runtime/lib:/var/task:/var/task/lib \
+    AWS_EXECUTION_ENV=AWS_Lambda_dotnetcore2.0 \
+    DOTNET_SDK_VERSION=2.1.3 \
+    DOTNET_CLI_TELEMETRY_OPTOUT=1 \
+    NUGET_XMLDOC_MODE=skip
+
+RUN rm -rf /var/runtime /var/lang && \
+  curl https://lambci.s3.amazonaws.com/fs/dotnetcore2.0.tgz | tar -zx -C / && \
+  yum install -y libunwind && \
+  curl https://dot.net/v1/dotnet-install.sh | bash -s -- -v $DOTNET_SDK_VERSION -i /var/lang/bin && \
+  mkdir /tmp/warmup && \
+  cd /tmp/warmup && \
+  dotnet new && \
+  cd / && \
+  rm -rf /tmp/warmup /tmp/NuGetScratch
+
+CMD ["dotnet", "build"]