(chocolateyGH-357) Change modifier for method

So that the method to get_all_installed_packages can be consumed from
elsewhere in the codebase.  This meant extending the interface for
INugetService to include this method as well, otherwise, a concrete
reference to an instance of NuGetService would be required, which is not
available.

src/chocolatey/infrastructure.app/services/INugetService.cs

@@ -17,6 +17,7 @@
 namespace chocolatey.infrastructure.app.services
 {
     using System.Collections.Concurrent;
+    using System.Collections.Generic;
     using configuration;
     using results;
 
@@ -58,5 +59,11 @@ public interface INugetService : ISourceRunner
         /// <param name="packageName">Name of the package.</param>
         void remove_rollback_directory_if_exists(string packageName);
 
+
+        /// <summary>
+        ///   Get all installed packages
+        /// </summary>
+        /// <param name="config">The configuration</param>
+        IEnumerable<PackageResult> get_all_installed_packages(ChocolateyConfiguration config);
     }
 }

src/chocolatey/infrastructure.app/services/NugetService.cs

@@ -1551,7 +1551,7 @@ public virtual void remove_installation_files(IPackage removedPackage, Chocolate
             }
         }
 
-        private IEnumerable<PackageResult> get_all_installed_packages(ChocolateyConfiguration config)
+        public IEnumerable<PackageResult> get_all_installed_packages(ChocolateyConfiguration config)
         {
             //todo : move to deep copy for get all installed
             //var listConfig = config.deep_copy();