Extend image behavior

[gitbls]

Currently, sdm by default extends the image by --xmb MB when you use sdm to customize the image. I've been burned a few times by this behavior, where sdm extends the image when I really didn't want it to.

I could change MY usage of sdm to do the extend separately and always use --noextend when I'm customizing the image.
OR
I could change sdm to make --noextend the default and require a specific switch to extend the image before doing customization.

Since this would affect users, and potentially scripts, posting this here to see if anyone has an opinion one way or the other.

Thanks for your thoughts on this.

[gitbls]

Here's what I decided to do:

• --extend will extend an image by --xmb N MB. --extend with --customize extends image and then customizes, if --extend is used without --customize, sdm will extend the image and exit
• If --extend is not specified, no image extend will be done
• --customize is now required to customize an image