TEST-74-AUX-UTILS.introspect-cli: simplify how --introspect-cli is tested

After c9cd66ee3a and
c81b5d36b9, the comment about systemd-backlight
and systemd-veritysetup was outdated. We can test them as any other program.

Also, use an array to make list easier to extend in the future and
adjust $PATH so we don't need to care about the split between public
and non-public programs.

test/units/TEST-74-AUX-UTILS.introspect-cli.sh

@@ -3,9 +3,27 @@
 set -eux
 set -o pipefail
 
-# Just a smoke test for the introspection code
-for i in systemd-ac-power systemd-analyze systemd-ask-password systemd-dissect \
-         systemd-id128 systemd-notify homectl resolvectl timedatectl varlinkctl; do
+# Some commands are in $PATH, others are in our private directory.
+# Check the other location too.
+PATH=$PATH:/usr/lib/systemd
+
+# A smoke test for the introspection code
+INTROSPECTABLE=(
+    homectl
+    resolvectl
+    systemd-ac-power
+    systemd-analyze
+    systemd-ask-password
+    systemd-backlight
+    systemd-dissect
+    systemd-id128
+    systemd-notify
+    systemd-veritysetup
+    timedatectl
+    varlinkctl
+)
+
+for i in "${INTROSPECTABLE[@]}"; do
     command -v "$i" >/dev/null || continue
 
     $i --introspect-cli | jq -e \
@@ -17,15 +35,6 @@ for i in systemd-ac-power systemd-analyze systemd-ask-password systemd-dissect \
     $i --intro | grep -e --help
 done
 
-# Those are not in $PATH and do not do regular option parsing, so the option must
-# be given verbatim
-for i in /usr/lib/systemd/systemd-backlight /usr/lib/systemd/systemd-veritysetup; do
-    [[ -x "$i" ]] || continue
-
-    $i --introspect-cli | jq -e \
-        '.mediaType == "application/vnd.io.systemd.cli-introspection-0"'
-done
-
 # systemd-id128 defines verbs, check that they are described
 systemd-id128 --introspect-cli | jq -e \
     '.commands[0].verbs | map(.names[0]) | contains(["new", "machine-id", "show", "help"])'