Running rzc without build server does not include errors

[pranavkm]

1. Add a parser error to a cshtml file
2. Run dotnet build /p:UseRazorBuildServer=false

Expected:
Shows parser diagnostics

Actual:
A failure exit code without any parser diagnostics.

The bug's here: https://github.com/aspnet/Razor/blob/master/src/Microsoft.AspNetCore.Razor.Tools/Program.cs#L44-L47. In the Server equivalent, the command returns the output to the caller which is printed to the output. This is missing in the standalone case.