libvirt_vm: set_console_getty() check for systemd

In RHEL7 (and at as of at least f18), the output for /etc/inittab has
changed, thus the existing search doesn't work resulting in the unnecessary
modification of /etc/inittab on the guest.
Merge pull request #1434 from jferlan/console_inittab

libvirt_vm: set_console_getty() check for systemd