Allow configure aws.iam_instance_profile_name

[keymon]

Allow define the aws.iam_instance_profile_name by setting the
environment variable $BOSH_LITE_INSTANCE_PROFILE_NAME

[cfdreddbot]

Hey keymon!

Thanks for submitting this pull request! I'm here to inform the recipients of the pull request that you and the commit authors have already signed the CLA.

[keymon]

Note: I did not really test this, I was discussing it with my colleague and we edited it on the fly in github.

But it should work fine and it can be merged. ;)

[keymon]

Hi, any news about this?

[cppforlife]

@keymon i've just got a build thru though we've lost our virtualbox builder (hence somewhat manual interaction required). have you considered using github.com/cloudfoundry/bosh-deployment to install bosh-lite? (example: https://github.com/cloudfoundry/bosh-deployment/blob/master/test.sh#L141)