p-m: rename to piuparts-master-backend.py

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-m: add new wrapper script piuparts-master

realize this as a shell script that reads piuparts.conf to
get paths and avoid having the slave needing to know these

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-s/p-m: pass section via stdin instead of command line

master: this will allow restricting the ssh key from the slave
to run a fixed command that does not take arguments

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-s/p-m: move chdir and stderr logging to master wrapper

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-s: simplify ssh command

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-s: stop using master-directory

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-s: stop using (master's) log-file

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p.conf: use simple master-command

running piuparts from git cannot easily restrict the command to be run via
authorized_keys

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-s.deb: restrict slave's ssh key to only allow running piuparts-master

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-s: support empty master command

the command may be set in authorized_keys

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