Fixing versions

- Added --version-suffix to build and publish
- Support reading DOTNET_* version variables everywhere versions can be read
- Show the commit sha in dotnet --version
- Added tests that check the assembly output version
- Set DOTNET_BUILD_VERSION when producing the CLI app itself so that it has the version information stamped in for help.

src/dotnet/commands/dotnet-help/HelpCommand.cs

@@ -27,7 +27,7 @@ Common Commands:
   run           Compiles and immediately executes a .NET project
   repl          Launch an interactive session (read, eval, print, loop)
   pack          Creates a NuGet package";
-        private static readonly string ProductVersion = GetProductVersion();
+        public static readonly string ProductVersion = GetProductVersion();
 
         private static string GetProductVersion()
         {