fix(pipelines) allow specification of buildImage in ShellScriptAction

The codebuild image of the ShellScriptAction was hardcoded. Some validation scripts require a different codebuild image.
This commit adds a property to the ShellScriptAction class to specify the image, which defaults to linux_4_0 (the current hardcoded value).
fixes aws#10919

packages/@aws-cdk/pipelines/lib/validation/shell-script-action.ts

@@ -54,6 +54,13 @@ export interface ShellScriptActionProps {
    */
   readonly additionalArtifacts?: codepipeline.Artifact[];
 
+  /**
+   * The CodeBuild image used for the build.
+   *
+   * @default LinuxBuildImage.STANDARD_4_0
+   */
+  readonly buildImage?: codebuild.IBuildImage
+
   /**
    * RunOrder for this action
    *
@@ -177,7 +184,7 @@ export class ShellScriptAction implements codepipeline.IAction, iam.IGrantable {
     }
 
     this._project = new codebuild.PipelineProject(scope, 'Project', {
-      environment: { buildImage: codebuild.LinuxBuildImage.STANDARD_4_0 },
+      environment: { buildImage: this.props.buildImage || codebuild.LinuxBuildImage.STANDARD_4_0 },
       vpc: this.props.vpc,
       securityGroups: this.props.securityGroups,
       subnetSelection: this.props.subnetSelection,

packages/@aws-cdk/pipelines/test/validation.test.ts

@@ -1,5 +1,6 @@
 import { anything, arrayWith, deepObjectLike, encodedJson } from '@aws-cdk/assert';
 import '@aws-cdk/assert/jest';
+import * as codebuild from '@aws-cdk/aws-codebuild';
 import * as codepipeline from '@aws-cdk/aws-codepipeline';
 import * as ec2 from '@aws-cdk/aws-ec2';
 import * as iam from '@aws-cdk/aws-iam';
@@ -330,6 +331,33 @@ test('run ShellScriptAction with Security Group', () => {
   });
 });
 
+test('run ShellScriptAction with specified codebuild image', () => {
+  // WHEN
+  pipeline.addStage('Test').addActions(new cdkp.ShellScriptAction({
+    actionName: 'imageAction',
+    additionalArtifacts: [integTestArtifact],
+    commands: ['true'],
+    buildImage: codebuild.LinuxBuildImage.STANDARD_2_0,
+  }));
+
+  // THEN
+  expect(pipelineStack).toHaveResourceLike('AWS::CodePipeline::Pipeline', {
+    Stages: arrayWith({
+      Name: 'Test',
+      Actions: [
+        deepObjectLike({
+          Name: 'imageAction',
+        }),
+      ],
+    }),
+  });
+  expect(pipelineStack).toHaveResourceLike('AWS::CodeBuild::Project', {
+    Environment: {
+      Image: 'aws/codebuild/standard:2.0',
+    },
+  });
+});
+
 class AppWithStackOutput extends Stage {
   public readonly output: CfnOutput;