Improve error messaging when locating tools fails

The subprocess run of `dotnet list package` didn't have exit code
checking, so it'd fail silently if anything inside dotnet fell over.
For better experience, check the exit code of dotnet and throw if it's
not zero, additionally appending stdout from the command
for convenience.

I hit this locally in testing other changes. Cause of failure was
incorrect working directory spec.

Program.cs

@@ -678,13 +678,17 @@ private static string getToolPath(string packageName, string toolExecutable)
         {
             var process = Process.Start(new ProcessStartInfo("dotnet", "list osu.Desktop.Deploy.csproj package")
             {
-                RedirectStandardOutput = true
+                RedirectStandardOutput = true,
+                RedirectStandardError = true,
             });
 
             Debug.Assert(process != null);
 
             process.WaitForExit();
 
+            if (process.ExitCode != 0)
+                throw new InvalidOperationException($"Could not locate tool {toolExecutable}!\nStandard error: {process.StandardError.ReadToEnd()}");
+
             string output = process.StandardOutput.ReadToEnd();
 
             var match = Regex.Matches(output, $@"(?m){packageName.Replace(".", "\\.")}.*\s(\d{{1,3}}\.\d{{1,3}}\.\d.*?)$");