[KNIFE-154] Support IAM Instance Profiles

http://tickets.opscode.com/browse/KNIFE-154

This pull request adds support for IAM Instance Profiles in the following ways:
 * ec2 server create gains an option: --iam-profile-name
 * ec2 server list gains a column, showing the assigned profile (if any)
 * ec2 server delete prints the profile name in the pre-deletion prompt

This pull request also contains an unrelated commit to fix a bug that currently exists on master.
I'm happy to rebase this branch against a fixed master when it is available.