Fix Python3 str decode issues (sonic-net#14332)

What is the motivation for this PR?
This fixes an issue due to Python 3 migration, where decode() is no longer a method of str.

How did you do it?
For cases where we actually need the unicode-escape conversion, I convert to bytes first, then re-decode to str to decode the escape sequences. In other cases where we are just taking the raw output of a command, I just removed the decode().

How did you verify/test it?
I ran the relevant sonic-mgmt tests and verified that the tests now pass and no longer raise exceptions due to decode() not being a method of str or AnsibleUnsafeText.

tests/common/helpers/sonic_db.py

@@ -169,7 +169,7 @@ def get_keys(self, table):
             raise SonicDbKeyNotFound("No keys for %s found in sonic-db cmd: %s" % (table, cmd))
         else:
             if six.PY2:
-                return result['stdout'].decode('unicode-escape')
+                return result['stdout'].decode('unicode-escape').splitlines()
             else:
                 return result['stdout'].splitlines()
 

tests/voq/test_voq_init.py

@@ -124,8 +124,10 @@ def test_voq_local_port_create(duthosts, enum_frontend_dut_hostname, enum_asic_i
 
     show_intf = asic.show_interface(command="status", include_internal_intfs=True)['ansible_facts']
     for portkey in keylist:
-        portkey = portkey.decode('unicode-escape')  # need to handle the hyphen in the inband port name
-        port_name = hostif_table[portkey]['value']["SAI_HOSTIF_ATTR_NAME"].decode('unicode-escape')
+        # need to handle the hyphen in the inband port name
+        portkey = bytes(portkey, encoding='ascii').decode('unicode-escape')
+        port_name = bytes(hostif_table[portkey]['value']["SAI_HOSTIF_ATTR_NAME"],
+                          encoding='ascii').decode('unicode-escape')
         port_state = hostif_table[portkey]['value']["SAI_HOSTIF_ATTR_OPER_STATUS"]
         port_type = hostif_table[portkey]['value']["SAI_HOSTIF_ATTR_TYPE"]
 
@@ -206,8 +208,8 @@ def check_voq_interfaces(duthosts, per_host, asic, cfg_facts):
         if porttype == 'hostif':
             # find the hostif entry to get the physical port the router interface is on.
             hostifkey = asicdb.find_hostif_by_portid(portid)
-            hostif = asicdb.get_hostif_table(refresh=False)[hostifkey][
-                'value']['SAI_HOSTIF_ATTR_NAME'].decode('unicode-escape')
+            hostif = bytes(asicdb.get_hostif_table(refresh=False)[hostifkey][
+                'value']['SAI_HOSTIF_ATTR_NAME'], encoding='ascii').decode('unicode-escape')
             logger.info("RIF: %s is on local port: %s", rif, hostif)
             rif_ports_in_asicdb.append(hostif)
             if hostif not in dev_intfs and hostif not in voq_intfs: