Improve some error messages

Rework the error handling to show where an error
occured during the run. While we are here, convert
these error messages to print to the log rather
than stdout.

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)
+			log.Printf("Couldn't start fakemachine: %v\n", err)
 			context.State = debos.Failed
 			return
 		}
 		if exitcode != 0 {
+			log.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) {
+			log.Printf("Could not create rootdir: %v\n", err)
 			context.State = debos.Failed
 			return
 		}