BUG: WebHostBuilder.UseEnvironment being overwritten on WebHostBuilder.Build

[giggio]

If you set the environment using WebHostBuilder.UseEnvironment and later call WebHostBuilder.Build it will initialize using HostingEnvironmentExtensions:
https://github.com/aspnet/Hosting/blob/1.0.0-beta5/src/Microsoft.AspNet.Hosting/WebHostBuilder.cs#L101
This will overwrite the setting applied with UseEnvironment, making this method useless.
Either remove the method, or rewrite the way it is working so that on Build the environment passed in by the user is used.

[davidfowl]

@giggio Care to submit a pull request?

/cc @HaoK

[giggio]

@davidfowl sure. I will change it in a way that the Build method works.

[davidfowl]

/cc @pakrym can you take a look?