p-m: support switching the logfile while master is running

start with logging to stderr and loglevel INFO until a section
logfile is opened

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-m: consolidate section initialization in Section

move section initialization from main() into Section

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-m: gracefully handle missing sections

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-m: add "section" command to master-slave protocol

Adds support for selecting the section inside the protocol
instead of requiring a command line parameter.
Forbid all other commands as long as no section was selected.

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-m: allow switching sections without reconnecting

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-s: use the "section" command to request a section

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-m: don't take a section argument from the command line

obsoleted by the new "section" command

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-m: don't exit after selecting a busy or unknown section

allow another section command to try the next section

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-s: don't pass command line arguments to master

superseded by the "section" command

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-s/p-m: document the new "section" command

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>
Merge commit '5f5547c5ce9143326c1d47c8a6862f5fc4f670aa' into develop