Customize ssh_timeout and ssh_retries

[ekrupnik]

This pull request is related to allowing a user to customize the sleep and retries mentioned in @sethvargo's open issue: test-kitchen/test-kitchen#422. The defaults given were what the code currently has:

ssh_timeout: 1
ssh_retries: 3

and neither are required to be set.

To customize, a .kitchen.yml would look like:

---
driver_plugin: ec2
driver_config:
  ssh_timeout: 15
  ssh_retries: 5
  aws_access_key_id: 'YOUR VALUE'
  aws_secret_access_key: 'YOUR VALUE'
  availability_zone: "us-east-1a"
...
more config here
...

[berniedurfee]

Yes please...