allow per-host sudo operation

Hi,
I'd like to introduce two new per-host sudo configuration variables for inventory. Use case: Apply same tasks for Fedora EC2 instances and Fedora Physical hosts. Since Cloud-Init prevents direct root log-in, the easiest option is to introduce a EC2 group in inventory to apply proper sudo settings for hosts that need it.
Suggested variables:
 - ansible_sudo
 - ansible_sudo_user

See also Issue #2678.

Thanks,
milan