Dev

The PR involves all the work to move HDInsight service SDK code base to Central Azure SDK repo in Github.

This will be a two phase migration:
1. Included in this PR: Move existing HDInsight code base to Azure SDK for net repo and provide build, publishing and test scripts for the code that we own.
2. (Not covered in this PR) Adopt the Hayak REST client generation for the HDI Rest Layer. Will be done in subsequent releases.

Summary:
1. We are following the sub directory structure for HDInsight where the REST and Convenience layers are all now moved into a new sub directory for our service under \azure-sdk-for-net\src\HDInsight
2. New build scripts are provided for HDInsight where it is required to capture behavior that is specific to our team, while leveraging common build scripts in all possible cases to ensure we are always on the latest Azure build scripts when possible.
3. New sln file azure-sdk-for-net\HDInsightManagementLibraries.sln builds all our projects.
4. New build script azure-sdk-for-net\HDInsightLibraries.msbuild is similar to libraries.msbuild, and is added to ensure the common build script is not affected and this would build, package, runs unit tests and publish only HDInsight specific packages to Nuget.
That way other management libraries don’t have to build our code and vice versa.
5. The src files under \azure-sdk-for-net\src\HDInsight are to a great extent a copy of the existing code base that is hosted in our source control system and has been shipping out publicly for more than a year now.
 
Jenkins:
We have a separate Jenkins jobs that is setup just for HDInsight specific sub directory. Some of the high level job description
 - HDI job to  dev full build, build packages and run tests
-  HDI job to build and publish packages to private feed (test and private feed)
-  HDI job to build and publish packages to NuGet feed.

 



This looks nearly identical to nuget.targets. Please merge.