As I reworked the push options, a bug got introduced where a duplication
of push in the config for the DNS dhcp-options would make it to fail.
There was no tests covering this, so I did not catch it earlier.
I've add the missing tests and fix the bug
So I was trying to push a route to my client and the script failed with
'too many arguments', I reworked this part and took the opportunity to
rework a little bit the way push and routes were handled.
I also added some tests and validated that what I changed would not
break what was there before.
