[ci] Fix the SONiC version starting with HEAD issue

[xumia]

Why I did it

Fix the SONiC version starting with HEAD issue. For example, sonic-broadcom-HEAD.40620469-1d98d18cf.bin.

How I did it

Allow the azure pipelines to input the correct branch name to overwrite the default HEAD value.

How to verify it

$ git branch 
* (HEAD detached at ca072d2)
$ sonic_get_version
HEAD.0-ca072d2
export BRANCH_NAME=201911
$ sonic_get_version
201911.0-ca072d2

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)

[qiluo-msft]

branch_name

Do you know why the old code does not work? Is the local folder under git control?

[xumia]

When checking out code, the azure pipeline checkout task does not set the local branch name, looks like the azure pipelines not support it very well. But azure pipeline provides a environment variable build.SourceBranchName, it tells which branch the code checked-out from.

Azure Pipelines:
$ git branch -vv
(HEAD detached at ca072d2) ca072d2 Disable CI/CD trigger
vmss-soni00007E:/agent/_work/1/s$ git rev-parse --abbrev-ref HEAD
HEAD

Jenkins:
jenkins-worker-2:/data/johnar/workspace/broadcom/buildimage-brcm-all$ git branch -vv
master 32b5b02 [sonic-platform-daemons] Update submodule (#7277)
jenkins-worker-2:/data/johnar/workspace/broadcom/buildimage-brcm-all$ git rev-parse --abbrev-ref HEAD
master

[lguohan]

it is better to address this from the azp script. otherwise, we have to cherry-pick this pr all the way to 201811 branch.

[lguohan]

@xumia, can you close this pr if it is not needed?