Add support for data sources

[cesar-rodriguez]

When using data sources, terraform-validate fails tests.

Example:

variable "environment" {}
variable "vpc_id" {}
variable "port" {}

data "aws_vpc" "selected" {
  id = "${var.vpc_id}"
}

resource "aws_security_group" "sg" {
  name        = "test"
  description = "test security group"
  vpc_id      = "${var.vpc_id}"

  ingress {
    from_port = "${var.port}"
    to_port   = "${var.port}"
    protocol  = "tcp"

    cidr_blocks = ["${data.aws_vpc.selected.cidr_block}"]
  }
}

Results:
ERROR: test_aws_security_group_inline_rule_open (terrascan.test_security_group.TestSecurityGroups)

Traceback (most recent call last):
File "/tmp/build/51a4a4ac/terrascan/terrascan/test_security_group.py", line 45, in test_aws_security_group_inline_rule_open
'cidr_blocks').list_should_not_contain('0.0.0.0/0')
File "/usr/local/lib/python3.6/site-packages/terraform_validate/terraform_validate.py", line 167, in list_should_not_contain
actual_property_value = self.validator.substitute_variable_values_in_string(property.property_value)
File "/usr/local/lib/python3.6/site-packages/terraform_validate/terraform_validate.py", line 504, in substitute_variable_values_in_string
variable_default_value = self.get_terraform_variable_value(a.variable)
File "/usr/local/lib/python3.6/site-packages/terraform_validate/terraform_validate.py", line 493, in get_terraform_variable_value
raise TerraformVariableException("There is no Terraform variable '{0}'".format(variable))
terraform_validate.terraform_validate.TerraformVariableException: There is no Terraform variable ''

[cesar-rodriguez]

This is no longer an issue as of Terrascan v1.0.0