test: Fix augeas test for macOS, improve test debuggability

- resolve a discrepancy in augeas behaviour on macOS
- on macOS `sed` requires an argument for `-i`.
- made the test fail as early as it can
- provide information about why the test is failing

test/shell/augeas-1.sh

@@ -12,19 +12,34 @@ mkdir -p "${MGMT_TMPDIR}"
 # run empty graph, with prometheus support
 $timeout --kill-after=60s 55s "$MGMT" run --tmp-prefix --yaml=augeas-1.yaml &
 pid=$!
+
+# kill server on error
+trap 'kill -SIGINT "$pid"' EXIT
+
 sleep 10s	# let it converge
 
-grep "X11Forwarding no" "${MGMT_TMPDIR}"sshd_config
+# make an exception on macOS as augeas behaves differently
+if [[ $(uname) == "Darwin" ]] ; then
+	value=false
+else
+	value=no
+fi
 
-sed -i "s/no/yes/" "${MGMT_TMPDIR}"sshd_config
+# make it easier to see why the test failed
+set -x
+cat "${MGMT_TMPDIR}"sshd_config
+
+grep "X11Forwarding ${value}" "${MGMT_TMPDIR}"sshd_config
+
+sed -i '' "s/${value}/yes/" "${MGMT_TMPDIR}"sshd_config
 
 grep "X11Forwarding yes" "${MGMT_TMPDIR}"sshd_config
 
 sleep 10s	# Augeas is slow
 
-grep "X11Forwarding no" "${MGMT_TMPDIR}"sshd_config
-
+grep "X11Forwarding ${value}" "${MGMT_TMPDIR}"sshd_config
 
+trap '' EXIT
 killall -SIGINT mgmt	# send ^C to exit mgmt
 wait $pid	# get exit status
 exit $?