rework lal upgrade for other backends and make it safer

[clux]

Currently disabled due to the hard dependency on artifactory.

There's a tiny window where you can screw up your upgrade (during extraction, which takes 0.1s normally). Should fix this properly when it's re-introduced.

Earlier output:

lal::upgrade: You are running 3.0.5 at /usr/local/bin/lal

lal::upgrade: Upgrading..
lal::upgrade: Downloading tarball to /usr/local/lal.tar
lal::upgrade: Backing up /usr/local/bin/lal to /usr/local/bin/lal/_lal_old
lal::upgrade: Unpacking new version of lal into /usr/local
lal::upgrade: lal upgraded successfully to 3.1.1 at /usr/local/bin/lal