apt changes some of its state/cache also if it errors out, most of
the time, so we actually want to print both, stderr and stdout.
Further, only warn if its exit code is non-zero, for the same
rationale, it may bring updates available even if it errors (e.g.,
because a future pbs-enterprise repo is additionally configured but
not accessible).
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
b282557563