Enable docker support for centos builds

- Added an option '--buildindocker <osname>' to build.sh
- Fixed bug which caused packaging to be skipped by default.
- Fixed bug which caused tarballs to be generated twice.
- Fixed bug to propagate build params(like debug, nopackage) to docker build.

scripts/docker/ubuntu/Dockerfile

@@ -0,0 +1,50 @@
+#
+# Copyright (c) .NET Foundation and contributors. All rights reserved.
+# Licensed under the MIT license. See LICENSE file in the project root for full license information.
+#
+
+# Dockerfile that creates a container suitable to build dotnet-cli
+FROM ubuntu:14.04
+
+# This could become a "microsoft/coreclr" image, since it just installs the dependencies for CoreCLR (and stdlib)
+# Install CoreCLR and CoreFx dependencies
+RUN apt-get update && \
+    apt-get -qqy install unzip curl libicu-dev libunwind8 gettext libssl-dev libcurl3-gnutls zlib1g liblttng-ust-dev lldb-3.6-dev lldb-3.6 
+
+# Install Dotnet CLI dependencies.
+# clang is required for dotnet-compile-native
+RUN apt-get -qqy install clang-3.5
+
+# Install Build Prereqs
+RUN echo "deb http://llvm.org/apt/trusty/ llvm-toolchain-trusty-3.6 main" | tee /etc/apt/sources.list.d/llvm.list && \
+    curl http://llvm.org/apt/llvm-snapshot.gpg.key | apt-key add - && \
+    apt-get update && \
+    apt-get install -y debhelper build-essential devscripts git cmake
+
+# Use clang as c++ compiler
+RUN update-alternatives --install /usr/bin/c++ c++ /usr/bin/clang++-3.5 100
+RUN update-alternatives --set c++ /usr/bin/clang++-3.5
+
+# Install azure cli. We need this to publish artifacts.
+RUN apt-get -y install nodejs-legacy && \
+    apt-get -y install npm && \
+    npm install -g azure-cli
+
+
+RUN apt-get install -qqy sudo
+
+# Setup User to match Host User, and give superuser permissions
+ARG USER_ID=0
+RUN useradd -m code_executor -u ${USER_ID} -g sudo
+RUN echo 'code_executor ALL=(ALL) NOPASSWD:ALL' >> /etc/sudoers
+
+# With the User Change, we need to change permssions on these directories
+RUN chmod -R a+rwx /usr/local
+RUN chmod -R a+rwx /home
+RUN chmod -R 755 /usr/lib/sudo
+
+# Set user to the one we just created
+USER ${USER_ID}
+
+# Set working directory
+WORKDIR /opt/code