[bug] Fix build wrapper commands not cleanup issue

[xumia]

Why I did it

Need to cleanup the build commands after build finished.

We had a timeout issue where preload firmware:
sonic:~$ sudo /tmp/anpscripts/preload_firmware sonic-aboot-broadcom-20201231.beta.15.swi http://10.20.17.0/firmware/ACS/sonic-aboot-broadcom-20201231.beta.15.swi af124e131bd18e4d66af90935b0d5bac

The timeout is caused by following command started by build command
/usr/bin/curl -Lks http://10.20.17.0/firmware/ACS/sonic-aboot-broadcom-20201231.beta.15.swi | md5sum | cut -d' ' -f1

Why timeout?
It is caused by using the wrong interface, need add "--interface eth0" in curl, it takes more than 1 hours to complete the command if not using the right interface.

sonic:~$ curl -f 'http://10.20.17.0/firmware/ACS/sonic-aboot-broadcom-20201231.beta.15.swi' -o sonic-aboot-broadcom-20201231.beta.15.swi
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  7  974M    7 73.7M    0     0   262k      0  1:03:14  0:04:47  0:58:27  296k

How I did it

Remove the build commands before make the squash fs.

How to verify it

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012

Description for the changelog

A picture of a cute animal (not mandatory but encouraged)