Every run we are doing a full tar.gz of the chroot environment that
never gets used.
It's not suitable for CI since we use fresh images each time there.
The cache in general isn't really isn't a very safe thing to have
around, because there's no invalidation procedure and no real way to
make one -- we've no guarantee that a new chroot build even moments
after a previous one wouldn't bring in or different packages, etc (of
course this is *unlikely*, but the longer you go between builds the
worse the problem becomes. Also, tons of packages get installed after
this not from any cache, so potential speed-up is rather marginal.
Debian turned this off with I58fc485aacacaa17243bf9ce760ed91256d1f182.
However, given the reasons above and it's complete lack of testing, I
don't see this as useful.
If we really want this type of thing, I think we should come up with a
way to use a persistent external yum/dnf cache that yum/dnf keeps in
sync with it's usual invalidation rules.
Change-Id: I66789c35db75c41bc45ea1ad2e26f87456de4e4d
4585955a8b