Prepend to RestoreSources: BuildTools may set it
Prepend to RestoreSources: BuildTools may set it

This property group used to be before the import, and a change that moved it after broke this scenario. Instead of moving it back, change it to match what CoreFX is doing for maintainability.

MichaelSimons/core-setup,weshaggard/core-setup,crummel/dotnet_core-setup,steveharter/core-setup,wtgodbe/core-setup,crummel/dotnet_core-setup,chcosta/core-setup,chcosta/core-setup,weshaggard/core-setup,ericstj/core-setup,crummel/dotnet_core-setup,steveharter/core-setup,chcosta/core-setup,chcosta/core-setup,crummel/dotnet_core-setup,weshaggard/core-setup,wtgodbe/core-setup,MichaelSimons/core-setup,rakeshsinghranchi/core-setup,ericstj/core-setup,rakeshsinghranchi/core-setup,wtgodbe/core-setup,weshaggard/core-setup,weshaggard/core-setup,crummel/dotnet_core-setup,ericstj/core-setup,steveharter/core-setup,steveharter/core-setup,rakeshsinghranchi/core-setup,rakeshsinghranchi/core-setup,crummel/dotnet_core-setup,wtgodbe/core-setup,rakeshsinghranchi/core-setup,rakeshsinghranchi/core-setup,MichaelSimons/core-setup,weshaggard/core-setup,ericstj/core-setup,ericstj/core-setup,wtgodbe/core-setup,MichaelSimons/core-setup,chcosta/core-setup,MichaelSimons/core-setup,wtgodbe/core-setup,steveharter/core-setup,steveharter/core-setup,chcosta/core-setup,ericstj/core-setup,MichaelSimons/core-setup