[NuGet] Fix dependencies not updated when updating solution packages.

Fixed bug 24276 - Updating NuGet packages for new Xamarin.Forms
project does not install Xamarin.Android.Support.v13
https://bugzilla.xamarin.com/show_bug.cgi?id=24276

The existing Xamarin.Forms project template uses an older version of
Xamarin.Android.Support.v4 which does not depend on
Xamarin.Android.Support.v13. The latest Xamarin.Android.Support.v4
does depend on Xamarin.Android.Support.v13. When updating the
Xamarin.Android.Support.v4 NuGet package installed by the existing
Xamarin.Forms project template the Xamarin.Android.Support.v13 NuGet
package was not installed in a project that targets MonoAndroid 3.2
when all the packages in the solution were updated (right click
solution and select Update NuGet Packages). If the
Xamarin.Android.Support.v4 NuGet package was updated itself (right
click the package and select Update) or if all the packages for the
project were updated (right click Packages folder and select Update)
then Xamarin.Android.Support.v13 NuGet package would be installed.

The problem was the NuGet package update was not set to update any
NuGet package dependencies when updating all packages in the solution.
Updating all packages in the project or the NuGet package individually
was set to update package dependencies.