[gcu][dhcp_relay] Fix dhcp_relay container is not running in gcu test (…

…#16460)

What is the motivation for this PR?
In gcu dhcp_relay test, it would add 2 vlans with 4 dhcp servers. Previously all 8 dhcp servers are added by cli separately, it would restart dhcp_relay container 8 times, which would cause dhcp_relay container is not running in gcu test in some low performance devices.

How did you do it?
Use sonic-db-cli to add dhcp servers, then manually resetart dhcp_relay container once.

How did you verify/test it?
Run tests

tests/common/dhcp_relay_utils.py

@@ -0,0 +1,16 @@
+from tests.common.helpers.assertions import pytest_assert
+from tests.common.utilities import wait_until
+
+
+def restart_dhcp_service(duthost):
+    duthost.shell('systemctl reset-failed dhcp_relay')
+    duthost.shell('systemctl restart dhcp_relay')
+    duthost.shell('systemctl reset-failed dhcp_relay')
+
+    def _is_dhcp_relay_ready():
+        output = duthost.shell('docker exec dhcp_relay supervisorctl status | grep dhcp | awk \'{print $2}\'',
+                               module_ignore_errors=True)
+        return (not output['rc'] and output['stderr'] == '' and len(output['stdout_lines']) != 0 and
+                all(element == 'RUNNING' for element in output['stdout_lines']))
+
+    pytest_assert(wait_until(120, 1, 10, _is_dhcp_relay_ready), "dhcp_relay is not ready after restarting")

tests/generic_config_updater/test_dhcp_relay.py

@@ -9,6 +9,8 @@
 from tests.common.gu_utils import generate_tmpfile, delete_tmpfile
 from tests.common.gu_utils import format_json_patch_for_multiasic
 from tests.common.gu_utils import create_checkpoint, delete_checkpoint, rollback_or_reload, rollback
+from tests.common.dhcp_relay_utils import restart_dhcp_service
+
 
 pytestmark = [
     pytest.mark.topology('t0', 'm0'),
@@ -108,16 +110,14 @@ def default_setup(duthost, vlan_intfs_list):
     # Generate 4 dhcp servers for each new created vlan
     for vlan in vlan_intfs_list:
         expected_content_dict[vlan] = []
+        cmds.append('sonic-db-cli CONFIG_DB hset "VLAN|Vlan{}" "dhcp_servers@" "{}"'
+                    .format(vlan, ",".join(["192.0.{}.{}".format(vlan, i) for i in range(1, 5)])))
         for i in range(1, 5):
-            cmds.append('config vlan dhcp_relay add {} 192.0.{}.{}'.format(vlan, vlan, i))
             expected_content_dict[vlan].append('192.0.{}.{}'.format(vlan, i))
 
     duthost.shell_cmds(cmds=cmds)
 
-    pytest_assert(
-        duthost.is_service_fully_started('dhcp_relay'),
-        "dhcp_relay service is not running during setup"
-    )
+    restart_dhcp_service(duthost)
 
     logger.info("default setup expected_content_dict {}".format(expected_content_dict))
     for vlanid in expected_content_dict: