eve-tag option is confusing with name

[deitch]

When you use the option --eve-tag (or config var eve.tag), it always appends -kvm-amd64 to the name.

Unless you know this, you can get very confused as to why it keeps saying it cannot find the image.

Docs must be changed to reflect it.

[rvs]

Huge +1 to this @deitch!