Wip/multiple if

Hello, 
Please find below the changes : 

* Handle multiple interfaces with one run.
The interface definition is a string composed as  follows : 
hostifname:ip_addr/netmask@gateway:containerifname
* Create vlan automatically if it doesn't exist
* Add custom routes on container if needed
* Use getopt for variables parsing
* Change usage

Thanks to @gquintard for his code review.

Regards,
Smana