Terraform 0.12+ index can be string or number

In the case of when mixing resources into the statefile in terraform, it's now
possible to have indexes that are not always int. In the example below using the
new 0.12 syntax `foreach` will result in the index being mapped to the
`each.key` name instead of the integer indexes.

```
variable "test" {
  default = {"testa" = "1.1.1.1", "testb" = "2.2.2.2"}
}

resource "aws_route53_record" "this" {
  for_each = var.test
  zone_id = "abc"
  name    = "${each.key}.tv."
  type    = "A"
  ttl     = "300"
  records = [each.value]
}
```

parser.go

@@ -65,7 +65,7 @@ type moduleStateTerraform0dot12 struct {
 }
 type resourceStateTerraform0dot12 struct {
 	Address   string                 `json:"address"`
-	Index     *int                   `json:"index"` // only set by Terraform for counted resources
+	Index     *interface{}           `json:"index"` // only set by Terraform for counted resources
 	Name      string                 `json:"name"`
 	RawValues map[string]interface{} `json:"values"`
 	Type      string                 `json:"type"`
@@ -324,7 +324,17 @@ func (s *stateTerraform0dot12) resources() []*Resource {
 			}
 			resourceKeyName := rs.Type + "." + modulePrefix + rs.Name
 			if rs.Index != nil {
-				resourceKeyName += "." + strconv.Itoa(*rs.Index)
+				i := *rs.Index
+				switch v := i.(type) {
+				case int:
+					resourceKeyName += "." + strconv.Itoa(v)
+				case float64:
+					resourceKeyName += "." + strconv.Itoa(int(v))
+				case string:
+					resourceKeyName += "." + v
+				default:
+					fmt.Fprintf(os.Stderr, "Warning: unknown index type %v\n", v)
+				}
 			}
 
 			// Terraform stores resources in a name->map map, but we need the name to

parser_test.go

@@ -943,6 +943,35 @@ const exampleStateFileTerraform0dot12 = `
 						}
 					}
 				},
+				{
+				  "address": "aws_route53_record.this",
+				  "mode": "managed",
+				  "type": "aws_route53_record",
+				  "name": "this",
+				  "index": "testb",
+				  "provider_name": "aws",
+				  "schema_version": 2,
+				  "values": {
+					"alias": [],
+					"allow_overwrite": null,
+					"failover_routing_policy": [],
+					"fqdn": "testb.tv",
+					"geolocation_routing_policy": [],
+					"health_check_id": null,
+					"id": "abc.tv._A",
+					"latency_routing_policy": [],
+					"multivalue_answer_routing_policy": null,
+					"name": "testb.tv",
+					"records": [
+					  "2.2.2.2"
+					],
+					"set_identifier": null,
+					"ttl": 300,
+					"type": "A",
+					"weighted_routing_policy": [],
+					"zone_id": "abc"
+				  }
+				},
 				{
 					"address": "vsphere_tag.bar",
 					"mode": "managed",