sudo should be optional

[dsevilla]

Hello:

There are systems where you can add any user to the docker group, so "sudo" is not necessary in order to run containers or build them. It would be nice to add some parameter to the script to specify if using sudo. It could be done easily using an internal variable to call docker either as 'docker' or 'sudo docker'.

I'm about to create a fork for that, as I don't want to execute in my system docker as root.

Could that be included in the current version?
Regards,
diego.