wait-for-emulator: don't prepend "unknown"

This way, error lines like this one:

    Waiting for emulator to start: unknown: error: no devices found

Become:

    Waiting for emulator to start: error: no devices found

tools/wait-for-emulator

@@ -16,7 +16,7 @@ explain() {
 	elif [[ "$1" =~ "running" ]]; then
 		printf "booting"
 	else
-		printf "unknown: $1"
+		printf "$1"
 	fi
 }
 
@@ -31,10 +31,9 @@ while true; do
 	if [[ "$out" =~ "stopped" ]]; then
 		break
 	fi
-	exp=$(explain "$out")
 	let "r = sec % 5"
 	if [[ $r -eq 0 ]]; then
-		echo "Waiting for emulator to start: $exp"
+		echo "Waiting for emulator to start: $(explain "$out")"
 	fi
 	sleep 1
 	let "sec++"