Rather than trying to enumerate tasks or track an ever changing cur_role
flag in PlayIterator, this change simply sets a flag on the last block in
the list of blocks returned by Role.compile(). The PlayIterator then checks
for that flag when the cur_block number is incremented, and marks the role
as complete if the given host had any tasks run in that role.
Fixes#20224
(cherry picked from commit cae682607c)
b12256acf2