Improve some error messages

Rework the error handling to show where an error
occured during the run.

Signed-off-by: Christopher Obbard <chris.obbard@collabora.com>

cmd/debos/debos.go

@@ -163,7 +163,7 @@ func main() {
 		// attempt to create a fakemachine
 		m, err = fakemachine.NewMachineWithBackend(options.Backend)
 		if err != nil {
-			log.Printf("error creating fakemachine: %v", err)
+			log.Printf("Couldn't create fakemachine: %v", err)
 
 			/* fallback to running on the host unless the user has chosen
 			 * a specific backend */
@@ -318,11 +318,12 @@ func main() {
 
 		exitcode, err := m.RunInMachineWithArgs(args)
 		if err != nil {
-			fmt.Println(err)
+			fmt.Printf("Couldn't start fakemachine: %v\n", err)
 			context.State = debos.Failed
 			return
 		}
 		if exitcode != 0 {
+			fmt.Printf("fakemachine failed with non-zero exitcode: %d\n", exitcode)
 			context.State = debos.Failed
 			return
 		}
@@ -354,6 +355,7 @@ func main() {
 	if _, err = os.Stat(context.Rootdir); os.IsNotExist(err) {
 		err = os.Mkdir(context.Rootdir, 0755)
 		if err != nil && os.IsNotExist(err) {
+			fmt.Printf("Could not create rootdir: %v\n", err)
 			context.State = debos.Failed
 			return
 		}