Updated cell scheduling section for Compute

Added mute_child, scheduler_retries, and scheduler_retry_delay options. Restructured section. Updated 'nova' -> 'Compute' in Cell Configuration Options section.

Partial-Bug: #1187290

Change-Id: I98902d24b5d161136e9efe6c84cf776e19b48742
Merge "Updated cell scheduling section for Compute"