Fix Updated govet Checks

[bflad]

Description

golangci-lint has updated the govet tool, which is showing a few valid check failures, e.g.

aws/config_test.go:14:14: composites: `github.com/terraform-providers/terraform-provider-aws/vendor/github.com/hashicorp/aws-sdk-go-base.MockRequest` composite literal uses unkeyed fields (govet)
      Request: &awsbase.MockRequest{"POST", "/", "Action=DescribeAccountAttributes&" +
                ^
aws/config_test.go:16:15: composites: `github.com/terraform-providers/terraform-provider-aws/vendor/github.com/hashicorp/aws-sdk-go-base.MockResponse` composite literal uses unkeyed fields (govet)
      Response: &awsbase.MockResponse{200, test_ec2_describeAccountAttributes_response, "text/xml"},
                 ^
aws/resource_aws_db_instance.go:1549:10: nilness: impossible condition: nil != nil (govet)
    if err != nil {
           ^
aws/resource_aws_docdb_cluster_instance.go:461:10: nilness: impossible condition: nil != nil (govet)
    if err != nil {
           ^
aws/resource_aws_egress_only_internet_gateway.go:42:9: nilness: impossible condition: nil != nil (govet)
  if err != nil {
         ^
aws/resource_aws_emr_security_configuration_test.go:70:10: nilness: tautological condition: non-nil != nil (govet)
    if err != nil {
           ^
aws/resource_aws_gamelift_game_session_queue_test.go:60:9: nilness: impossible condition: nil != nil (govet)
  if err != nil {
         ^
aws/resource_aws_organizations_account_test.go:74:26: nilness: nil dereference in field selection (govet)
    if resp == nil && resp.Account != nil {
                           ^
aws/resource_aws_organizations_policy_test.go:108:26: nilness: nil dereference in field selection (govet)
    if resp == nil && resp.Policy != nil {
                           ^
aws/resource_aws_vpn_connection_test.go:229:11: nilness: tautological condition: non-nil != nil (govet)
      if err != nil {
             ^
aws/resource_aws_vpn_gateway_test.go:386:11: nilness: tautological condition: non-nil != nil (govet)
      if err != nil {
             ^

Action Items

• Fix new govet failures
• Re-run broken TravisCI builds

[ghost]

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