Change vol label and detach iso

* Changed Volume Label from TAILSLIVECD to TAILSLIVE because it’s not a
CD (and TAILSLIVEUSB is too long).
* detach the tails iso when finished with it
turn off debug and move all download operations

* Commented out trace (debugging) command (`set -w`)
* Removed `-k` switch from command that downloads iso because `-k`
turns off cert checking, but it’s not even using https
* Removed URL definitions from start because they are now automatically
figured out, and they need to use curl now so should only really be
done in `download_tails()`
* Moved signature and key downloading to `download_tails()` because
they required internet access and if the files were already in the data
directory, they need not be performed, whereas `verify_tails()` always
is.