fix(coreos-install): Fix compatibility with older versions.
fix(coreos-install): Fix compatibility with older versions.

When adding proper support for selecting release channels I forgot to
add the special case to make `-V alpha` continue to work.

Fixes https://github.com/coreos/bugs/issues/29

zhang0137/init,BugRoger/init,nicescale/init,endocode/init,zhang0137/init,BugRoger/init,coreos/init,coreos/init,nicescale/init,endocode/init,coreos/init