extracted stages and task in cli task tracking

moving towards refactoring all of event log renderer

Signed-off-by: dmitriy kalinin <dmitriy@pivotallabs.com>
Add tests for task duration.

Signed-off-by: Matthew Boedicker <mboedicker@pivotallabs.com>
Do not stub new on total duration.

Test public methods which are delegated to TotalDuration but treat
TotalDuration as an implementation detail.

Signed-off-by: Matthew Boedicker <mboedicker@pivotallabs.com>
Add duration for finished and failed tasks to output.

Signed-off-by: Matthew Boedicker <mboedicker@pivotallabs.com>
Add callback for stage started, stage finished and stage failed.
Add duration method to Stage.
Added stage callbacks.

Reorganized event log renderer specs.

Signed-off-by: Matthew Boedicker <mboedicker@pivotallabs.com>