Merge pull request #15662 from hpidcock/fix-relation-departing-test

#15662

Fixes 5s sleep being inadequate. Instead polls debug-log up to 10 times with 10s delay.

## QA steps

Apply this patch
```
diff --git a/testcharms/charms/departer/hooks/self-relation-departed b/testcharms/charms/departer/hooks/self-relation-departed
index 241c4f724d..b04dd07dc8 100644
--- a/testcharms/charms/departer/hooks/self-relation-departed
+++ b/testcharms/charms/departer/hooks/self-relation-departed
@@ -1,6 +1,8 @@
 #!/bin/sh
 echo $0

+sleep 30
+
 remote_unit=$(echo $JUJU_REMOTE_UNIT)
 departing_unit=$(echo $JUJU_DEPARTING_UNIT)
```

Run the test
```
./main.sh -v -s '"test_relation_data_exchange,test_relation_list_app"' relations test_relation_departing_unit`
```

## Documentation changes

N/A

## Bug reference

https://jenkins.juju.canonical.com/job/test-relations-test-relation-departing-unit-lxd/591/consoleText

testcharms/charms/departer/metadata.yaml

@@ -5,7 +5,4 @@ peers:
   self:
     interface: dummy
 series:
-  - xenial
-  - bionic
-  - focal
   - jammy

tests/suites/relations/relation_departing_unit.sh

@@ -17,21 +17,34 @@ run_relation_departing_unit() {
 
 	echo "Remove departer/1"
 	juju remove-unit departer/1
-	sleep 5
-
-	echo "Check departer/1 is departing the relation"
-	got=$(juju debug-log --replay --include unit-departer-0 | grep 'Remote unit departer/1 is departing the relation' || true)
-	if [ -z "${got}" ]; then
-		# shellcheck disable=SC2046
-		echo $(red "expected departer/0 to be notified that departer/1 went away")
-		exit 1
-	fi
-	got=$(juju debug-log --replay --include unit-departer-1 | grep 'Local unit is departing the relation' || true)
-	if [ -z "${got}" ]; then
-		# shellcheck disable=SC2046
-		echo $(red "expected departer/1 to be notified that it is going away")
-		exit 1
-	fi
+
+	attempt=10
+	while [[ ${attempt} -gt 0 ]]; do
+		attempt=$((attempt - 1))
+		sleep 10
+		echo "Check departer/1 is departing the relation"
+		got=$(juju debug-log --replay --include unit-departer-0 | grep 'Remote unit departer/1 is departing the relation' || true)
+		if [ -z "${got}" ]; then
+			# shellcheck disable=SC2046
+			echo $(red "expected departer/0 to be notified that departer/1 went away")
+			if [[ ${attempt} -eq 0 ]]; then
+				exit 1
+			else
+				continue
+			fi
+		fi
+		got=$(juju debug-log --replay --include unit-departer-1 | grep 'Local unit is departing the relation' || true)
+		if [ -z "${got}" ]; then
+			# shellcheck disable=SC2046
+			echo $(red "expected departer/1 to be notified that it is going away")
+			if [[ ${attempt} -eq 0 ]]; then
+				exit 1
+			else
+				continue
+			fi
+		fi
+		break
+	done
 
 	destroy_model "${model_name}"
 }