[KNIFE_EC2-62] Add support for IAM instance profiles.

'server create' gains an option, --iam-profile-name

'server list' output contains an extra column to show the profile name
(if one has been assigned).

'server delete' shows the profile name assigned to the instance being
deleted.
[KNIFE-154] Rename --iam-profile-name to --iam-profile.
[KNIFE-154] Remove unnecessary details from stubbed EC2 instance IAM attribute.
[KNIFE-154] Don't print IAM profile unless specified.

This applies to create/delete - list retains a column for IAM profile.