Add empty-init code-smell script. (#18406)

Also removed boilerplate from otherwise empty __init__.py files
which should not contain any code (checked by empty-init script).

test/sanity/code-smell/empty-init.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+found=''
+
+for path in lib/ansible/modules/ test/units/; do
+    files=$(find "${path}" -name __init__.py -size '+0')
+
+    if [ "${files}" ]; then
+        echo "${files}"
+        found=1
+    fi
+done
+
+if [ "${found}" ]; then
+    echo "One or more __init__.py file(s) listed above are non-empty."
+    exit 1
+fi