Improve error reporting for nested exceptions

[conanthedev]

Unhandled exception. SimpleExec.ExitCodeException: The command exited with code 1.
   at SimpleExec.Command.RunAsync(ProcessStartInfo startInfo, Boolean noEcho, String echoPrefix, Func`2 handleExitCode, CancellationToken cancellationToken) in /_/SimpleExec/Command.cs:line 228
   at SimpleExec.Command.RunAsync(String name, String args, String workingDirectory, Boolean noEcho, String echoPrefix, Action`1 configureEnvironment, Boolean createNoWindow, Func`2 handleExitCode, CancellationToken cancellationToken) in /_/SimpleExec/Command.cs:line 158
   at Program.<Main>$(String[] args) in D:\a\Xenial.BTool\Xenial.BTool\Xenial.BTool\Program.cs:line 7
   at Program.<Main>(String[] args)