If tty_handler() resets terminal while pkttyagent is run in background job,
the process gets stopped by SIGTTOU. This impacts systemctl, hence it must
be blocked for a while and then the process gets killed anyway.
Upstream commit: 28e3a6653d8c3777b07e0128a0d97d46e586e311
Signed-off-by: Adam Duskett <Aduskett@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>