tests: add signal receiver program

Target to kill with a check that will be written later.

CC: Bernhard Voelker <mail@bernhard-voelker.de>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
tests: check kill is converting signals names correctly

CC: Bernhard Voelker <mail@bernhard-voelker.de>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
tests: check various ways to specify kill signal

CC: Bernhard Voelker <mail@bernhard-voelker.de>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
tests: check kill print pid option

CC: Bernhard Voelker <mail@bernhard-voelker.de>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
tests: check kill all user processes

CC: Bernhard Voelker <mail@bernhard-voelker.de>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
kill: add --verbose option to display what is killed

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
lib/procutils: reset errno before strtol() call

When going through /proc the last entry made readdir() to alter errno,
which made the strtol() to think something went wrong, resulting kill(1)
tests to fail when running in --parallel mode.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>