Remove Aboot.iso dependencies and updated versions to 4.21.0F

[tigpas]

I had some trouble with vEOS-lab-4.20.1F-virtualbox.box from Arista download center, so I found this Git and build my own 4.21.0F without trouble. On this way, I didn't understand why we need the Aboot.iso, so I removed it and it's working.

To test the exsisting VagrantFiles, I updated the version number on all places to the same version, so we can do more copy/paste.

Thank you for this GIT and feel free to merge this PR.