Fix Grafana Kiosk to use killall

Fbi seems to fork and continue on another process, as the shown process ID does not
match the returned value. Use killall to fix this problem.

Note that this only works because nobody else is using fbi on the system.

templates/hobbes/kiosk.sh.j2

@@ -16,10 +16,11 @@ fbi_pid=0
 # Function to be executed on SIGTERM
 on_sigterm() {
     echo "SIGTERM received, exiting..."
-    # Kill the fbi process with the stored PID
-    if [ $fbi_pid -ne 0 ]; then
-        sudo kill $fbi_pid
-    fi
+
+    # Kill the fbi process
+    # As the process forks itself, we do not get a reliable PID and killall is needed
+    killall fbi
+
     # Remove the temporary file
     rm -f /tmp/grafana.png
     exit 0
@@ -34,13 +35,8 @@ do
     mosquitto_sub -h $BROKER -t $TOPIC -C 1 > /tmp/grafana.png
 
     # Kill the previous fbi process
-    if [ $fbi_pid -ne 0 ]; then
-        sudo kill $fbi_pid
-    fi
-
-    # Display the image using fbi
-    fbi -T 1 -noverbose -a /tmp/grafana.png &
-    fbi_pid=$!
+    # As the process forks itself, we do not get a reliable PID and killall is needed
+    killall fbi
 
     # Wait to avoid a race condition between
     # fbi starting and mosquitto truncating the file