Fix syntax errors in an OpenStack example script
[GH-2793] Exclude examples from documented methods

Example code in various providers directories is getting picked up by
Yard when documenting such that a number of global constants and helpers
are appearing to be part of fog.

This excludes them using `.yardopts`

It also excludes generated documentation from provider subdirectories
from git.
Merge pull request #2795 from L2G/openstack-example-syntax-err

Fix syntax errors in an OpenStack example script
Adding support for IAM roles and STS in the AWS::IAM service