Set packer_http_addr of extra-vars as an empty string when it's nil

[126ium]

Fixes #173. This fix involves examining the generatedData to determine if the PackerHTTPAddr is nil. If the PackerHTTPAddr is nil, set it as an empty string. This modification ensures the proper handling of the packer_http_addr variable within the ansible-local provisioner.

Test

1. Navigate to the source directory of Ansible-local.
2. Run the test cases as follows:

[ansible-local]$ go test
2023/09/13 14:38:13 ui: Provisioning with Ansible...
2023/09/13 14:38:13 ui: Creating Ansible staging directory...
2023/09/13 14:38:13 ui: Creating directory: /tmp/packer-provisioner-ansible-local/65013cb5-9e19-0c3d-9ee7-ca232dba2af5
2023/09/13 14:38:13 ui: Uploading playbook file: /tmp/2605838767
2023/09/13 14:38:13 ui: Creating directory: /tmp/packer-provisioner-ansible-local/65013cb5-9e19-0c3d-9ee7-ca232dba2af5/tmp
2023/09/13 14:38:13 ui: Uploading playbook file: /tmp/239453821
2023/09/13 14:38:13 ui: Creating directory: /tmp/packer-provisioner-ansible-local/65013cb5-9e19-0c3d-9ee7-ca232dba2af5/tmp
2023/09/13 14:38:13 ui: Uploading playbook file: /tmp/1305372664
2023/09/13 14:38:13 ui: Creating directory: /tmp/packer-provisioner-ansible-local/65013cb5-9e19-0c3d-9ee7-ca232dba2af5/tmp
2023/09/13 14:38:13 ui: Uploading inventory file...
2023/09/13 14:38:13 ui: Executing Ansible: cd /tmp/packer-provisioner-ansible-local/65013cb5-9e19-0c3d-9ee7-ca232dba2af5 &&  ANSIBLE_FORCE_COLOR=1 PYTHONUNBUFFERED=1 ansible-playbook /tmp/packer-provisioner-ansible-local/65013cb5-9e19-0c3d-9ee7-ca232dba2af5/tmp/2605838767 --extra-vars "packer_build_name= packer_builder_type= packer_http_addr= -o IdentitiesOnly=yes"  -c local -i /tmp/packer-provisioner-ansible-local/65013cb5-9e19-0c3d-9ee7-ca232dba2af5/packer-provisioner-ansible-local1541997294

packer_http_addr should be an empty string, not %!s(<nil>).

Closes #173

[lbajolet-hashicorp]

Hi @126ium,

Thanks for the PR!

I just left one comment regarding the usage of the option, I think that if it is unset, it is probably better to not include it in the extra args instead of leaving it empty, but that could be a valid use though, I'll let you tell me what you think.

Aside from that, it looks good to me, we can merge this once we've reached a decision on this.

Thanks again!

[lbajolet-hashicorp]

I would suggest maybe not adding the value to the extra-vars instead?
Unless this is used in the target, but then I would assume that it being empty would probably yield an error, so it may or may not be a good idea, what do you think?

[126ium]

Thanks for your reply and suggestion. Your idea is better. The ansible-playbook already provides a good handler for empty/default extra-vars, so I believe there will be no potential error. It's unnecessary to add them explicitly when they are empty.

I'm testing new codes with my module. Then I'll update this patch once I get any updates.