(MAINT) nits in beaker ec2 support 

- correctly identify zombies that are over X hours old
- better notification of what instances are being examined for possible
  termination
- properly notify user of missing aws_access_key_id and
  aws_secret_access_key during initialization
While I cannot find any direct documentation, all examples of ec2 LaunchTimes end in a 'Z' indicating UTC/GM time.  I believe that it is the standard.