Add a config reload command to create an initial config for L2 mode.

Step 1 in L2 config wiki actually serve the purpose of remove existing
minigraph config except for those that are absolutely necessary. We
should not skip that.

tests/l2/test_l2_configure.py

@@ -53,6 +53,24 @@ def test_l2_config_and_upgrade(request, duthosts, rand_one_dut_hostname, localho
     # Save original config
     duthost.shell("sudo cp {} {}".format(CONFIG_DB, CONFIG_DB_BAK))
     # Perform L2 configuration
+    mgmt_fact = duthost.get_extended_minigraph_facts()["minigraph_mgmt_interface"]
+    init_cfg = '''
+    cat <<EOF | sudo config reload /dev/stdin -y
+    {{
+        "MGMT_INTERFACE": {{
+            "eth0|{}/{}": {{
+                "gwaddr": "{}"
+            }}
+        }},
+        "DEVICE_METADATA": {{
+            "localhost": {{
+                "hostname": "{}"
+            }}
+        }}
+    }}
+    EOF
+    '''.format(mgmt_fact["addr"], mgmt_fact["prefixlen"], mgmt_fact["gwaddr"], duthost.hostname)
+    duthost.shell(init_cfg)
     l2_cfg = "sudo sonic-cfggen --preset l2 -p -H -k {}" \
         " | sudo config load /dev/stdin -y".format(hwsku)
     duthost.shell(l2_cfg)
@@ -71,7 +89,7 @@ def test_l2_config_and_upgrade(request, duthosts, rand_one_dut_hostname, localho
 
     # Step 4: Verifies no config fro minigraph is written into ConfigDB.
     try:
-        for table in ["TELEMETRY", "RESTAPI", "DEVICE_METADATA"]:
+        for table in ["TELEMETRY", "RESTAPI"]:
             count = int(duthost.shell('sonic-db-cli CONFIG_DB KEYS "{}|* | wc -l'.format(table))['stdout'])
             pytest_assert(count == 0, "{} table is not empty!".format(table))
     except Exception: