fix(lambda): use IRole instead of Role to allow imports (#1509)

In order to allow passing in an imported role to a Lambda/Alias,
we must use `IRole` instead of `Role`.

Author: Elad Ben-Israel

packages/@aws-cdk/aws-lambda/lib/alias.ts

@@ -71,7 +71,7 @@ export class Alias extends FunctionBase {
   /**
    * Role associated with this alias
    */
-  public readonly role?: iam.Role | undefined;
+  public readonly role?: iam.IRole | undefined;
 
   protected readonly canCreatePermissions: boolean = true; // Not used anyway
 

packages/@aws-cdk/aws-lambda/lib/lambda-ref.ts

@@ -33,7 +33,7 @@ export interface IFunction extends cdk.IConstruct, events.IEventRuleTarget, logs
   /**
    * The IAM role associated with this function.
    */
-  readonly role?: iam.Role;
+  readonly role?: iam.IRole;
 
   /**
    * Whether or not this Lambda function was bound to a VPC
@@ -123,7 +123,7 @@ export interface FunctionImportProps {
    *
    * If the role is not specified, any role-related operations will no-op.
    */
-  role?: iam.Role;
+  role?: iam.IRole;
 
   /**
    * Id of the securityGroup for this Lambda, if in a VPC.
@@ -149,7 +149,7 @@ export abstract class FunctionBase extends cdk.Construct implements IFunction  {
   /**
    * The IAM role associated with this function.
    */
-  public abstract readonly role?: iam.Role;
+  public abstract readonly role?: iam.IRole;
 
   /**
    * Whether the addPermission() call adds any permissions

packages/@aws-cdk/aws-lambda/lib/lambda.ts

@@ -111,7 +111,7 @@ export interface FunctionProps {
    * @default a unique role will be generated for this lambda function.
    * Both supplied and generated roles can always be changed by calling `addToRolePolicy`.
    */
-  role?: iam.Role;
+  role?: iam.IRole;
 
   /**
    * VPC network to place Lambda network interfaces
@@ -284,7 +284,7 @@ export class Function extends FunctionBase {
   /**
    * Execution role associated with this function
    */
-  public readonly role?: iam.Role;
+  public readonly role?: iam.IRole;
 
   /**
    * The runtime configured for this lambda.
@@ -493,7 +493,7 @@ export class Function extends FunctionBase {
 export class ImportedFunction extends FunctionBase {
   public readonly functionName: string;
   public readonly functionArn: string;
-  public readonly role?: iam.Role;
+  public readonly role?: iam.IRole;
 
   protected readonly canCreatePermissions = false;
 

packages/@aws-cdk/aws-lambda/lib/singleton-lambda.ts

@@ -37,7 +37,7 @@ export interface SingletonFunctionProps extends FunctionProps {
 export class SingletonFunction extends FunctionBase {
   public readonly functionName: string;
   public readonly functionArn: string;
-  public readonly role?: iam.Role | undefined;
+  public readonly role?: iam.IRole | undefined;
   protected readonly canCreatePermissions: boolean;
   private lambdaFunction: IFunction;