[202012][show] add new CLI to show tunnel route objects #2255

[zjswhhh]

What I did

Add new CLI support to show tunnel route objects in APP DB.

sign-off: Jing Zhang [email protected]

How I did it

• Check if tunnel route object exists for server_ipv4, server_ipv6. If existing, print it out.
• If not specifying port name, print all tunnel route objects.

How to verify it

• Added unit tests.
• Tested on dual testbeds:
  • show mux tunnel-route Ethernet140

     PORT         DEST_TYPE    DEST_ADDRESS    
     -----------  -----------  ---------------  
     Ethernet140  server_ipv4  192.168.0.29/32  
    

  • show mux tunnel-route --json Ethernet140

     {
         "TUNNEL_ROUTE": {
             "Ethernet140": {
                 "server_ipv4": {
                     "DEST": "192.168.0.29/32"
                 }
             }
         }
     }
    

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)

[zjswhhh]

Hi @theasianpianist - can you help review? It's to manually pick up PR #2255.