kni: avoid using lsb_release script

kni: avoid using lsb_release script

The lsb_release script is part of an optional package which is not
always installed. On the other hand, /etc/lsb-release is always present
even on minimal Ubuntu installations.

    root@ubuntu1604:~# dpkg -S /etc/lsb-release
    base-files: /etc/lsb-release

Read the file if present and use the variables defined in it.

Signed-off-by: Robin Jarry <robin.jarry@6wind.com>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>