Remove the base postfix from the internal task executor

There is no need to have a postfix of 'base' in the task
executor as it is obvious by having a metaclass of abc.ABCMeta
and the fact that it has no methods that the task executor base
is a base class and should be used as such without a 'base'
postfix to also signify the same information.

Change-Id: I1f5cbcd29f1453d68e774f9f9f733eb873efc7cb