When the same role is listed consecutively in a play, the previous role
completion detection failed to mark it as complete as it only checked to
see if the role changed.
This patch addresses that by also keeping track of which task in the role
we are on, so that even if the same role is encountered during later passes
the task number will be less than or equal to the last noted task position.
Related to #15409
test/units/plugins/action/test_action.py had code
for handling a bug in python 3.4's mock_open that
causes errors when reading binary data.
Moved to compat/tests/mock.py so other tests can
use it by default.
