confd: change failure mode hostname to capitals

For consistency with UNKNOWN base mac address, and making it easier for
the user to actually notice the fault condition.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/confd/share/failure.d/10-system.json

@@ -1,6 +1,6 @@
 {
     "ietf-system:system": {
-	"hostname": "failure",
+	"hostname": "FAILURE",
 	"authentication": {
 	    "user": [
 		{