systemd: Increase devices timeout in QEMU machines to avoid failures on serial-getty
Systemd serial-getty is failing because dev-tty ends with timeout, systemd
uses a default timeout of 90 secs that it's reached on AB's production environment
due to high I/O loads (nfs).
When use QEMU is used without KVM support, the machine code is executed by TCG
(software code execution) that is dependent on devices layer and causes locks
between TCG/Devices increasing the machine code execution time [1].
QEMU don't support configuration of device timeout always uses a default one that is
90 secs, so the next patch increases the device timeout to 240 secs [2] in order give
enough time to get devices ready. It ONLY applies on QEMU machines.
