pkg/types/aws/validation/platform: Include eu-north-1

RHCOS grew support for this in 905db73 (data/data/rhcos.json:
update the bootimage to 420.8.20190708.2 for CRI-O 1.14, 2019-07-03, openshift#1941).
And until we get something like [1], we need this not-very-DRY bump to
keep up.

[1]: openshift#1528

pkg/types/aws/validation/platform.go

@@ -24,13 +24,13 @@ var (
 		//"cn-north-1":     "Beijing",
 		//"cn-northwest-1": "Ningxia",
 		"eu-central-1": "Frankfurt",
-		//"eu-north-1":     "Stockholm",
-		"eu-west-1": "Ireland",
-		"eu-west-2": "London",
-		"eu-west-3": "Paris",
-		"sa-east-1": "São Paulo",
-		"us-east-1": "N. Virginia",
-		"us-east-2": "Ohio",
+		"eu-north-1":   "Stockholm",
+		"eu-west-1":    "Ireland",
+		"eu-west-2":    "London",
+		"eu-west-3":    "Paris",
+		"sa-east-1":    "São Paulo",
+		"us-east-1":    "N. Virginia",
+		"us-east-2":    "Ohio",
 		//"us-gov-east-1":  "AWS GovCloud (US-East)",
 		//"us-gov-west-1":  "AWS GovCloud (US-West)",
 		"us-west-1": "N. California",

pkg/types/validation/installconfig_test.go

@@ -408,7 +408,7 @@ func TestValidateInstallConfig(t *testing.T) {
 				}
 				return c
 			}(),
-			expectedError: `^platform\.aws\.region: Unsupported value: "": supported values: "ap-northeast-1", "ap-northeast-2", "ap-south-1", "ap-southeast-1", "ap-southeast-2", "ca-central-1", "eu-central-1", "eu-west-1", "eu-west-2", "eu-west-3", "sa-east-1", "us-east-1", "us-east-2", "us-west-1", "us-west-2"$`,
+			expectedError: `^platform\.aws\.region: Unsupported value: "": supported values: "ap-northeast-1", "ap-northeast-2", "ap-south-1", "ap-southeast-1", "ap-southeast-2", "ca-central-1", "eu-central-1", "eu-north-1", "eu-west-1", "eu-west-2", "eu-west-3", "sa-east-1", "us-east-1", "us-east-2", "us-west-1", "us-west-2"$`,
 		},
 		{
 			name: "valid libvirt platform",