Bug fix: #4011 #4012 - "show run acl", "show run interfaces" - traceback when no ACL_RULE/INTERFACE is present. (#4226)

* Fix bugs - "show run acl/interfaces" returns traceback when no ACL_RULE/INTERFACE is present in configuration
- Change logic in main to take data only if the var_json appears in DB.
- Add unit testing for bug fix & fix comments

Signed-off-by: Noa Or <noaor@mellanox.com>

src/sonic-config-engine/sonic-cfggen

@@ -295,7 +295,7 @@ def main():
         template = jinja2.Template('{{' + args.var + '}}')
         print(template.render(data))
 
-    if args.var_json != None:
+    if args.var_json != None and args.var_json in data:
         if args.key != None:
             print(json.dumps(FormatConverter.to_serialized(data[args.var_json], args.key), indent=4, cls=minigraph_encoder))
         else:

src/sonic-config-engine/tests/test_cfggen.py

@@ -331,3 +331,13 @@ class TestCfgGen(TestCase):
                 output = subprocess.check_output("sed -i \'s/%s/%s/g\' %s" % (BACKEND_TOR_ROUTER, TOR_ROUTER, self.sample_graph_simple), shell=True)
 
             self.test_jinja_expression(self.sample_graph_simple, TOR_ROUTER)
+
+    def test_show_run_acl(self):
+        argument = '-a \'{"key1":"value"}\' --var-json ACL_RULE'
+        output = self.run_script(argument)
+        self.assertEqual(output, '')
+
+    def test_show_run_interfaces(self):
+        argument = '-a \'{"key1":"value"}\' --var-json INTERFACE'
+        output = self.run_script(argument)
+        self.assertEqual(output, '')