Allow config shutdown and startup operations on valid PortChannel interface names (sonic-net#474)

* Avoid shutdown/startup commands on invalid interface names
* sonic-utilities: Fix bug in the show command to display a specific interface status
* sonic-utilities: Check for the presence of interface in port table instead of the optional alias attribute
* Addressed review comment for sonic-net#424
* Undone the change in intfutil file to push that fix in a seperate PR.
* Corrected the error message string for 'config interface <invalid-interface-name> tartup/shutdown'.
* [sonic-utilities] Fix to shutdown and startup on valid PortChannel interface names
* [sonic-utilities] Allow shutdown/startup commands to be done using the alias names of PORTs.

Author: kirankella

config/main.py

@@ -80,9 +80,9 @@ def interface_alias_to_name(interface_alias):
         for port_name in port_dict.keys():
             if interface_alias == port_dict[port_name]['alias']:
                 return port_name
-        click.echo("Invalid interface {}".format(interface_alias))
 
-    return None
+    # Interface alias not in port_dict, just return interface_alias
+    return interface_alias
 
 
 def interface_name_is_valid(interface_name):
@@ -91,6 +91,10 @@ def interface_name_is_valid(interface_name):
     config_db = ConfigDBConnector()
     config_db.connect()
     port_dict = config_db.get_table('PORT')
+    port_channel_dict = config_db.get_table('PORTCHANNEL')
+
+    if get_interface_naming_mode() == "alias":
+        interface_name = interface_alias_to_name(interface_name)
 
     if interface_name is not None:
         if not port_dict:
@@ -99,6 +103,10 @@ def interface_name_is_valid(interface_name):
         for port_name in port_dict.keys():
             if interface_name == port_name:
                 return True
+        if port_channel_dict:
+            for port_channel_name in port_channel_dict.keys():
+                if interface_name == port_channel_name:
+                    return True
     return False
 
 def interface_name_to_alias(interface_name):