Update execute/revert comments

The basetask revert/execute comments were updated to be more
clear and to remove the details about context (which no longer
is passed in) as well as to explain the kwargs passed into the
revert method and how and why they are provided.

Change-Id: Ie3abb1c73a526e35f37eb2636407dac983e7fcc4
Merge "Update execute/revert comments"