Check-instance-events.rb should be able to assume-role

[pmiles]

In a previous version, there used to be a -R flag for check-instance-events which allowed it to assume a different role.

In our environment, we have multiple different AWS accounts, and still need to be able to assume roles in different accounts in order to fully query our estate.

Can we re-implement the -R functionality.

   option :role,
         short:       '-R ASSUME_ROLE',
         long:        '--assume-role-arn ARN',
         description: 'IAM Role to assume'