test driver support

[deas]

System Information

Linux distribution

n/a

Terraform version

n/a

Provider and libvirt versions

v0.7.6

Checklist

n/a

Description of Issue/Question

For testing purposes, it would be nice if the Test "mock" driver could be made available.

Setup

n/a

Steps to Reproduce Issue

Use a system without the libvirt daemon running/listening at /var/run/libvirt/libvirt-sock.

$ export LIBVIRT_DEFAULT_URI = "test:///default"
$ terraform plan
....
 Error: failed to connect: dial unix /var/run/libvirt/libvirt-sock: connect: no such file or directory
...
$ virsh list
 Id   Name   State
----------------------
 1    test   running
$