First iteration of support for Java

fn/langs/dotnet.go

@@ -1,7 +1,6 @@
 package langs
 
 import (
-	"fmt"
 	"os"
 	"os/exec"
 )
@@ -34,7 +33,7 @@ func (lh *DotNetLangHelper) PreBuild() error {
 	cmd.Stderr = os.Stderr
 	cmd.Stdout = os.Stdout
 	if err := cmd.Run(); err != nil {
-		return fmt.Errorf("error running docker build: %v", err)
+		return dockerBuildError(err)
 	}
 	return nil
 }