Use friendly obsolete messages

[Tratcher]

https://github.com/aspnet/AspNetCore/wiki/Engineering-guidelines#breaking-changes

https://github.com/aspnet/Extensions/blob/d349703e08a14e7bcabec0f632bbff55f3c79b87/src/Hosting/Abstractions/src/EnvironmentName.cs#L9
https://github.com/aspnet/Extensions/blob/d349703e08a14e7bcabec0f632bbff55f3c79b87/src/Hosting/Abstractions/src/IApplicationLifetime.cs#L12
https://github.com/aspnet/Extensions/blob/d349703e08a14e7bcabec0f632bbff55f3c79b87/src/Hosting/Abstractions/src/IHostingEnvironment.cs#L12
https://github.com/aspnet/AspNetCore/blob/4451a804477f7f3d4d0ed89d56c51332d8c3ee25/src/Hosting/Abstractions/src/IHostingEnvironment.cs#L11
https://github.com/aspnet/AspNetCore/blob/4451a804477f7f3d4d0ed89d56c51332d8c3ee25/src/Hosting/Abstractions/src/IApplicationLifetime.cs#L11

@Eilon