Create a class to manage workflow data

* CLOUDBLD-8271

All workflow data are moved to a dedicated class. These data are
accessible via workflow.data attributes.

A new abstract class ISerialize is added to define the load/dump interface for
data classes referenced from the workflow data class and the data class itself.

New methods is_empty and __eq__ are added to some classes for writing
tests easily.

BuildResult class can be loaded and dumped as a normal attribute like others.
It's a little special than others due to the build step is not implemented yet,
no multi-arch build result object is handled.

Signed-off-by: Chenxiong Qi <[email protected]>

Author: tkdchen

.pylintrc

@@ -64,7 +64,8 @@ disable=I,
         useless-import-alias,  # nice to have
         useless-super-delegation,  # nice to have
         wrong-import-order,
-        wrong-import-position
+        wrong-import-position,
+        eq-without-hash  # no need to hash objects which have method __eq__
 
 [REPORTS]