[#7059] Improve tarball status UX

* Don't say 'Generating' when we're not
* Fail quickly when we know snapshot isn't being built

Signed-off-by: Tim Van Steenburgh <tvansteenburgh@gmail.com>
[#7059] Removed unnecessary status check on tarball download page

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>