Add msbuild plugin support.

This is a simple plugin to wrap msbuild tool, which is used
for building .NET projects.

Change-Id: I0803d4477d9132265e559ad40b8c1a981a2cd5ef
Reviewed-on: https://review.openstack.org/27654
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins