show interface status <interface-name> throws error (fixes sonic-net#427) (sonic-net#440)

* sonic-utilities: Bug fix while showing interface status for a specific interface.

* While getting the keys from port table for a specific interface, wrong db is passed, fixed the bug

Signed-off-by: kiran.kella@broadcom.com

Author: kirankella

scripts/intfutil

@@ -39,7 +39,7 @@ def appl_db_keys_get(appl_db, intf_name):
     if intf_name is None:
         appl_db_keys = appl_db.keys(appl_db.APPL_DB, "PORT_TABLE:*")
     elif intf_name.startswith('Ethernet'):
-        appl_db_keys = db.keys(appl_db.APPL_DB, "PORT_TABLE:%s" % intf_name)
+        appl_db_keys = appl_db.keys(appl_db.APPL_DB, "PORT_TABLE:%s" % intf_name)
     else:
         return None