Explicitly log portal detections

Bug triagers are often confused by the log messages "validation failed
with redirect to X", thinking that this is an actual failure. As it is
expected to happen when a portal is detected, change the message to
"validation detected a portal with redirect to X".

Test: atest
Change-Id: I8655f30dbb4ada4537990d93a845994a4dfbe24b
1 file changed