Address Pull Request Feedback

- Suppress First-Time Run Messages
- Redirect Nuget Warmup Output
- Justify Nuget Warmup Procedure

build-image-src/Dockerfile-dotnetcore31

@@ -55,15 +55,19 @@ ENV DOTNET_ROOT=/var/lang/bin
 
 # Install .NET build tools
 
+# Suppress first-time output.
+ENV DOTNET_NOLOGO=true
+
 ENV PATH=/root/.dotnet/tools:$PATH \
     AWS_EXECUTION_ENV=AWS_Lambda_dotnetcore3.1 \
     DOTNET_CLI_TELEMETRY_OPTOUT=1 \
     NUGET_XMLDOC_MODE=skip
 
+# Warm up the nuget cache once now for faster startup on each use.
 RUN curl -L https://dot.net/v1/dotnet-install.sh | bash -s -- -c 3.1 -i "${DOTNET_ROOT}" && \
   mkdir /tmp/warmup && \
   cd /tmp/warmup && \
-  dotnet new && \
+  dotnet new > /dev/null && \
   cd / && \
   rm -rf /tmp/warmup /tmp/NuGetScratch /tmp/.dotnet