Recent modern operating systems commonly use systemd. Octavia no longer
supports very old version of Ubuntu/CentOS/Debian which use sysvinit or
upstart so supporting only systemd should be enough.
The remaining usage of the service command is replaced by the ones with
the systemctl command.
Change-Id: Ifc3f85bf280527c0f76b2c0e0db2be813249dafa
991e0da01e