Better metrics about sleep and group

Currently if a group includes a 10 second sleep we are going to say that the group took 10 seconds, which while correct might not be what the enduser is interested in. I propose that we:

1. implement #880
2. Have the group know that there was n seconds of sleep in it's current execution - probably through some new methods on lib.Group
3. Add new metric group_sleep?
4. Choose whether to remove the sleep time from the group_duration or add another metric that is the group_duration without the group_sleep or the reverse - have the group_duration be without the group_sleep but have another full_group_duration that includes the group_sleep