update_mdc: make --really a flag

Description

This was always meant to be used as --really, but due to an oversight, it had to be given a value, as in --really 1.

How Has This Been Tested?

Used the script.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the code style of this project.

Reviewers

@ahmedk @roscar