provider/docker: Fix flaky integration tests

Asserting on the value of `latest` on an image is prone to failing
because of new images being pushed upstream. Instead of asserting on a
hash, we assert that the value matches a regular expression for the
format of an image hash.

builtin/providers/docker/resource_docker_image_test.go

@@ -1,6 +1,7 @@
 package docker
 
 import (
+	"regexp"
 	"testing"
 
 	"github.com/hashicorp/terraform/helper/resource"
@@ -14,17 +15,14 @@ func TestAccDockerImage_basic(t *testing.T) {
 			resource.TestStep{
 				Config: testAccDockerImageConfig,
 				Check: resource.ComposeTestCheckFunc(
-					resource.TestCheckResourceAttr(
-						"docker_image.foo",
-						"latest",
-						"8dd8107abd2e22bfd3b45b05733f3d2677d4078b09b5edce56ee3d8677d3c648"),
+					resource.TestMatchResourceAttr("docker_image.foo", "latest", regexp.MustCompile(`\A[a-f0-9]{64}\z`)),
 				),
 			},
 		},
 	})
 }
 
-func TestAddDockerImage_private(t *testing.T) {
+func TestAccDockerImage_private(t *testing.T) {
 	resource.Test(t, resource.TestCase{
 		PreCheck:  func() { testAccPreCheck(t) },
 		Providers: testAccProviders,
@@ -32,10 +30,7 @@ func TestAddDockerImage_private(t *testing.T) {
 			resource.TestStep{
 				Config: testAddDockerPrivateImageConfig,
 				Check: resource.ComposeTestCheckFunc(
-					resource.TestCheckResourceAttr(
-						"docker_image.foobar",
-						"latest",
-						"2c40b0526b6358710fd09e7b8c022429268cc61703b4777e528ac9d469a07ca1"),
+					resource.TestMatchResourceAttr("docker_image.foobar", "latest", regexp.MustCompile(`\A[a-f0-9]{64}\z`)),
 				),
 			},
 		},