[multi-asic]: Add function to load database config (sonic-net#4112)

What is the motivation for this PR?
With the changes in sonic-net/sonic-buildimage#8173, the applications that connect to namespace dbs have to load global database configuration. Due to this change, the sonic-py-common.multi_asic functions that connect to database will fail if database configuration is not loaded in ansible library functions.

How did you do it?
Add a new module_utility library function to load the right db configuration based on single or multi-asic platform.
Invoke this function in port_util and lag_facts where mutli_asic library function is invoked which connects to db.

How did you verify/test it?
Bring up a multi-asic VS testbed.
./testbed-cli.sh -t vtestbed.csv -m veos_vtb -k ceos add-topo vms-kvm-four-asic-t1-lag password.txt
Before adding this change, failure seen while running test_bgp_fact.py

ansible/library/lag_facts.py

@@ -3,6 +3,7 @@
 import json
 import sys
 from ansible.module_utils.basic import *
+from ansible.module_utils.multi_asic_utils import load_db_config
 try:
     from sonic_py_common import multi_asic
     NAMESPACE_LIST = multi_asic.get_namespace_list()
@@ -63,6 +64,8 @@ def get_po_names(self):
         '''
             Collect configured lag interface names
         '''
+        # load db config
+        load_db_config()
         for ns in NAMESPACE_LIST:
             rt, out, err = self.module.run_command("sonic-cfggen -m /etc/sonic/minigraph.xml {} -v \"PORTCHANNEL.keys() | join(' ')\"".format('-n ' + ns if ns else ''))
             if rt != 0:

ansible/module_utils/multi_asic_utils.py

@@ -0,0 +1,22 @@
+def load_db_config():
+    '''
+    Load the correct database config file:
+     - database_global.json for multi asic
+     - database_config.json for single asic
+    Loading database config file is not required for
+    201911 images so ignore import error or function
+    name error.
+    '''
+    try:
+        from sonic_py_common import multi_asic
+        from swsscommon import swsscommon
+        if multi_asic.is_multi_asic():
+            if not swsscommon.SonicDBConfig.isGlobalInit():
+                swsscommon.SonicDBConfig.load_sonic_global_db_config()
+        else:
+            if not swsscommon.SonicDBConfig.isInit():
+                swsscommon.SonicDBConfig.load_sonic_db_config()
+    except ImportError:
+        pass
+    except NameError:
+        pass

ansible/module_utils/port_utils.py

@@ -15,6 +15,8 @@ def _port_alias_to_name_map_50G(all_ports, s100G_ports,):
 def get_port_alias_to_name_map(hwsku, asic_id=None):
     try:
         from sonic_py_common import multi_asic
+        from ansible.module_utils.multi_asic_utils  import load_db_config
+        load_db_config()
         namespace_list = multi_asic.get_all_namespaces()
         for key, list in namespace_list.items():
             asic_ids = []