[sonic-mgmt docker] - latest sonic-mgmt docker based on Ubuntu 20.04 can not install extra packets using APT

[ppikh]

Description

Latest sonic-mgmt docker based on Ubuntu 20.04 can not install extra packets using APT.
Old image based on Ubuntu 18.04 can install any packets by "apt update && apt install packet_name", new sonic-mgmt docker image can not do it and when we do "apt update && apt install packet_name" we got error.
This issue introduced by PR: #11831

Steps to reproduce the issue:

1. Run sonic-mgmt docker :docker run -it docker-sonic-mgmt bash
2. Change to sudo mode: sudo -s
3. Do: apt update
4. Try to install packet: apt install vim

Describe the results you received:

Can not install any packet using APT.

Reading package lists... Done
Building dependency tree       
Reading state information... Done
vim is already the newest version (2:8.1.2269-1ubuntu5.7).
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 python-ptf : Depends: python-scapy but it is not installable
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).

If do command: "apt --fix-broken install" it will remove packet "python-ptf" and then PTF tests will fail.

Describe the results you expected:

Possible to install packets using APT

Output of show version:

(paste your output here)

Output of show techsupport:

(paste your output here or download and attach the file here )

Additional information you deem important (e.g. issue happens only occasionally):

[yxieca]

@wangxin , @wsycqyz are you aware of this issue? Is there a fix? If not, let's revert the change and put it back with the fix?

[wsycqyz]

The dependencies packages need to be re-compile in Ubuntu20.04.
I have reverted PR#11831. Will raise another PR for Python3 migration later.

[wsycqyz]

Fix has been committed.