sfml - option to skip by site name or ID

[adambernstein]

The sfml command is extremely useful, but it would be better if there were an option to skip specified sites. I realize there's currently a way to skip by install profile, but that doesn't cover the majority of cases where we need to skip. It would be nice to extend this logic to a comma separated list of sites names/IDs like so:

drush @site.name sfml some-command --skip=site1,site2,site3

[vbouchet31]

#152

[sdelbosc]

I have just merged that one feel free to test further