use SL_ convention for env vars

[chulkilee]

You can pass in your username and api_key when creating a SoftLayer client instance. However, you can also set these in the environmental variables ‘SL_USERNAME’ and ‘SL_API_KEY’.

ref

I didn't make it support the previous env names (SOFTLAYER_*) intentionally, since 1) having different combination of SL and SOFTLAYER env can be confusing and 2) this plugin is not the "official" one and I think it's okay to make that change.

[leonidlm]

@chulkilee thank you for your contribution. Can you please clarify why you decided to rename the env variables?

You mentioned that "having different combination of SL and SOFTLAYER env can be confusing", however as far as I can tell I always used SOFTLAYER_ prefix in the code.

[chulkilee]

Oh, I was not clear - when I refer "official" one, it is official python softlayer client.

You can pass in your username and api_key when creating a SoftLayer client instance. However, you can also set these in the environmental variables ‘SL_USERNAME’ and ‘SL_API_KEY’.

ref

Although I may overwrite packer-builder-softlayer configuration using env via packer user env, it would be nice if two libraries pick up the configuration from the same env var.

[cmluciano]

Not sure if there was every any resolution on this, closing for now