fix C# distribtest dockerfiles

tools/dockerfile/distribtest/csharp_jessie_x64/Dockerfile

@@ -14,18 +14,15 @@
 
 FROM debian:jessie
 
-RUN apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
-RUN echo "deb http://download.mono-project.com/repo/debian wheezy main" | tee /etc/apt/sources.list.d/mono-xamarin.list
+RUN apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
+RUN echo "deb http://download.mono-project.com/repo/debian jessie main" | tee /etc/apt/sources.list.d/mono-official.list
 RUN echo "deb http://download.mono-project.com/repo/debian wheezy-apache24-compat main" | tee -a /etc/apt/sources.list.d/mono-xamarin.list
 RUN echo "deb http://download.mono-project.com/repo/debian wheezy-libjpeg62-compat main" | tee -a /etc/apt/sources.list.d/mono-xamarin.list
-RUN echo "deb http://download.mono-project.com/repo/debian wheezy-libtiff-compat main" | tee -a /etc/apt/sources.list.d/mono-xamarin.list
 
 RUN apt-get update && apt-get install -y \
     mono-devel \
     ca-certificates-mono \
-    nuget
+    nuget \
+    && apt-get clean
 
-# make sure we have nuget 2.12+ (in case there's an older cached docker image)
-RUN apt-get update && apt-get install -y nuget
-
-RUN apt-get update && apt-get install -y unzip
+RUN apt-get update && apt-get install -y unzip && apt-get clean

tools/dockerfile/distribtest/csharp_jessie_x86/Dockerfile

@@ -14,18 +14,15 @@
 
 FROM 32bit/debian:jessie
 
-RUN apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
-RUN echo "deb http://download.mono-project.com/repo/debian wheezy main" | tee /etc/apt/sources.list.d/mono-xamarin.list
+RUN apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
+RUN echo "deb http://download.mono-project.com/repo/debian jessie main" | tee /etc/apt/sources.list.d/mono-official.list
 RUN echo "deb http://download.mono-project.com/repo/debian wheezy-apache24-compat main" | tee -a /etc/apt/sources.list.d/mono-xamarin.list
 RUN echo "deb http://download.mono-project.com/repo/debian wheezy-libjpeg62-compat main" | tee -a /etc/apt/sources.list.d/mono-xamarin.list
-RUN echo "deb http://download.mono-project.com/repo/debian wheezy-libtiff-compat main" | tee -a /etc/apt/sources.list.d/mono-xamarin.list
 
 RUN apt-get update && apt-get install -y \
     mono-devel \
     ca-certificates-mono \
-    nuget
+    nuget \
+    && apt-get clean
 
-# make sure we have nuget 2.12+ (in case there's an older cached docker image)
-RUN apt-get update && apt-get install -y nuget
-
-RUN apt-get update && apt-get install -y unzip
+RUN apt-get update && apt-get install -y unzip && apt-get clean

tools/dockerfile/distribtest/csharp_ubuntu1604_x64/Dockerfile

@@ -17,11 +17,16 @@ FROM ubuntu:16.04
 RUN apt-get update && apt-get install -y \
     mono-devel \
     ca-certificates-mono \
-    nuget
+    nuget \
+    && apt-get clean
 
 # make sure we have nuget 2.12+ (in case there's an older cached docker image)
 RUN apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
 RUN echo "deb http://download.mono-project.com/repo/debian wheezy main" | tee /etc/apt/sources.list.d/mono-xamarin.list
-RUN apt-get update && apt-get install -y nuget
+RUN apt-get update && apt-get install -y nuget && apt-get clean
 
-RUN apt-get update && apt-get install -y unzip
+# Prevent "Error: SendFailure (Error writing headers)" when fetching nuget packages
+# See https://github.com/tianon/docker-brew-ubuntu-core/issues/86
+RUN apt-get update && apt-get install -y tzdata && apt-get clean
+
+RUN apt-get update && apt-get install -y unzip && apt-get clean