[image] Added "chain" command to fetch, load, and execute image

The "chain" command combines the functions of "imgfetch", "imgload",
and "boot".

    chain http://etherboot.org/gtest/gtest.gpxe

is equivalent to:

    kernel http://etherboot.org/gtest/gtest.gpxe
    boot

src/hci/commands/image_cmd.c

@@ -221,6 +221,22 @@ static int kernel_exec ( int argc, char **argv ) {
 	return 0;
 }
 
+/**
+ * The "imgauto" command
+ *
+ * @v argc		Argument count
+ * @v argv		Argument list
+ * @ret rc		Exit code
+ */
+static int imgauto_exec ( int argc, char **argv) {
+	int rc;
+
+	if ( ( rc = imgfetch_core_exec ( NULL, IMG_EXEC, argc, argv ) ) != 0 )
+		return rc;
+
+	return 0;
+}
+
 /**
  * "imgload" command syntax message
  *
@@ -546,6 +562,10 @@ struct command image_commands[] __command = {
 		.name = "kernel",
 		.exec = kernel_exec,
 	},
+	{
+		.name = "imgauto",
+		.exec = imgauto_exec,
+	},
 	{
 		.name = "imgload",
 		.exec = imgload_exec,