[autoboot] Ensure that an error message is always printed for a boot failure

The case of an unsupported SAN protocol will currently not result in
any error message.  Fix by printing the error message at the top level
using strerror(), rather than using hard-coded error messages in the
error paths.

src/arch/i386/interface/pcbios/aoeboot.c

 	memset ( &ata, 0, sizeof ( ata ) );
 	memset ( &drive, 0, sizeof ( drive ) );
 
-	printf ( "AoE booting from %s\n", root_path );
-
 	/* FIXME: ugly, ugly hack */
 	struct net_device *netdev = last_opened_netdev();
 

src/arch/i386/interface/pcbios/iscsiboot.c

 		goto err_alloc_drive;
 	}
 
-	printf ( "iSCSI booting from %s\n", root_path );
-
 	if ( ( rc = iscsi_attach ( scsi, root_path ) ) != 0 ) {
 		printf ( "Could not attach iSCSI device: %s\n",
 			 strerror ( rc ) );

src/usr/autoboot.c

 
 	/* Construct URI */
 	uri = parse_uri ( filename );
-	if ( ! uri ) {
-		printf ( "Out of memory\n" );
+	if ( ! uri )
 		return -ENOMEM;
-	}
 	filename_is_absolute = uri_is_absolute ( uri );
 	uri_put ( uri );
 	if ( ! filename_is_absolute ) {
 	}
 
 	image = alloc_image();
-	if ( ! image ) {
-		printf ( "Out of memory\n" );
+	if ( ! image )
 		return -ENOMEM;
-	}
 	if ( ( rc = imgfetch ( image, filename,
 			       register_and_autoload_image ) ) != 0 ) {
-		printf ( "Could not load %s: %s\n",
-			 filename, strerror ( rc ) );
 		goto done;
 	}
-	if ( ( rc = imgexec ( image ) ) != 0 ) {
-		printf ( "Could not boot %s: %s\n",
-			 filename, strerror ( rc ) );
+	if ( ( rc = imgexec ( image ) ) != 0 )
 		goto done;
-	}
 
  done:
 	image_put ( image );
 	fetch_string_setting ( NULL, &filename_setting, buf, sizeof ( buf ) );
 	if ( buf[0] ) {
 		printf ( "Booting from filename \"%s\"\n", buf );
-		return boot_next_server_and_filename ( next_server, buf );
+		if ( ( rc = boot_next_server_and_filename ( next_server,
+							    buf ) ) != 0 ) {
+			printf ( "Could not boot from filename \"%s\": %s\n",
+				 buf, strerror ( rc ) );
+			return rc;
+		}
+		return 0;
 	}
 	
 	/* No filename; try the root path */
 	fetch_string_setting ( NULL, &root_path_setting, buf, sizeof ( buf ) );
 	if ( buf[0] ) {
 		printf ( "Booting from root path \"%s\"\n", buf );
-		return boot_root_path ( buf );
+		if ( ( rc = boot_root_path ( buf ) ) != 0 ) {
+			printf ( "Could not boot from root path \"%s\": %s\n",
+				 buf, strerror ( rc ) );
+			return rc;
+		}
+		return 0;
 	}
 
 	printf ( "No filename or root path specified\n" );