p-s: clear idle state after sighup to continue asap

if there are unchecked packages after a sighup, try to rerun
this section as early as possible and finish the work

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-s: check load frequently and sleep if it exceeds threshold

tunable via [global] slave-load-max = 1.5
0 (default) disables
9.5 seems to be reasonable for 8 slaves running on 4 cores / 8 threads

Signed-off-by: Andreas Beckmann <anbe@debian.org>
slave_run: do not run the screen as root

Signed-off-by: Andreas Beckmann <anbe@debian.org>
use screen -ls to check for running screens

Signed-off-by: Andreas Beckmann <anbe@debian.org>
slave_join: use 'script /dev/null' to get a writable tty

avoid

user$ sudo su - piupartss
piupartss$ screen -x
Cannot open your terminal '/dev/pts/42' - please check.

Signed-off-by: Andreas Beckmann <anbe@debian.org>
slave_run: use piuparts.conf to get paths etc.

Signed-off-by: Andreas Beckmann <anbe@debian.org>
slave_run: ensure PIUPARTS_TMPDIR exists

Signed-off-by: Andreas Beckmann <anbe@debian.org>
slave_run: drop ancient trap+mail code

that's useless with daemonized screen

Signed-off-by: Andreas Beckmann <anbe@debian.org>