Make sure Terraform itself is not linked with libvix

[c4milo]

In order to compile terraform_vix from within Terraform we added some extra flags to Terraform's makefile. This is causing the terraform binary to be linked to libvix without being really necessary. It also makes it difficult for a user to use terraform as she would have to set the LD_LIBRARY_PATH to where libvix library exists in order to run Terraform. We need to make sure libvix is not linked to Terraform but only to the plugin. By doing this, we can set the LD_LIBRARY_PATH by our selves from Terraform, immediately before launching the vix plugin.

[c4milo]

This is fixed.