Support option --ports of config qos reload for reloading ports' QoS and buffer configuration to default

[stephenxs]

What I did

CLI: config qos reload --ports <ports_list>

• --ports <ports_list>: a set of interfaces with empty QoS and buffer configurations (typically they have just been created via DPB).
  Format: <port>{,port}, like “Ethernet0” or “Ethernet4,Ethernet5,Ethernet6,Ethernet7”
• Each port in the list should exist in the CONFIG_DB.PORT table

The flow:

1. Render the template qos_config.j2 and buffer_config.j2, generating a temporary json file. (This is one step in “config qos reload”).
2. Parse the json file, extracting all the items on the ports in the port_list
3. Apply all the extracted items into the CONFIG_DB

How I did it

How to verify it

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)

[liat-grozovik]

@neethajohn kindly reminder to review