ec2: check for changes

In the ec2 module, if an id is specified, check if there have been
any changes. If not, return changed=False

Fixes #3746
ec2: Removed unused line

Remove the reference to the unused "termination_list" parameter
in the ec2 module. The instance_ids parameter is the one that contains
the list of instance ids to be terminated.
Merge pull request #3747 from lorin/ec2-check

ec2: check for changes