tests/data-source/aws_organizations_organization: Add Organizations PreCheck

For consistency with other Organizations testing and to prevent the following failure:

```
       --- FAIL: TestAccAWSOrganizations/Organization/DataSource (3.55s)
            testing.go:568: Step 0 error: errors during apply:

                Error: Error creating organization: AlreadyInOrganizationException: The AWS account is already a member of an organization.
```

Acceptance testing from Organizations member account:

```
        --- SKIP: TestAccAWSOrganizations/Organization/DataSource (1.57s)
            provider_test.go:247: skipping tests; this AWS account must not be an existing member of an AWS Organization
```

Acceptance testing from standalone account:

```
        --- PASS: TestAccAWSOrganizations/Organization/DataSource (29.70s)
```

Author: bflad

aws/data_source_aws_organizations_organization_test.go

@@ -13,6 +13,7 @@ func testAccDataSourceAwsOrganizationsOrganization_basic(t *testing.T) {
 	resource.Test(t, resource.TestCase{
 		PreCheck: func() {
 			testAccPreCheck(t)
+			testAccOrganizationsAccountPreCheck(t)
 		},
 		Providers: testAccProviders,
 		Steps: []resource.TestStep{