Add do as a dynamic version of block.

[estheruary]

This is a big one but is a source of personal annoyance for me. This patch creates do as the dynamic equivalent of block. Some examples.

# You can loop over blocks!
- name: Loop over multiple tasks.
  do:
    - debug: msg=hello
    - debug: var=item
  loop: [1, 2, 3]

# What's different in this case is that it's not expanded by applying the when clause to each task. 
# With `block` you would see two skipped tasks while with this you will see one skipped `do`.
#
- name: Skip multiple tasks as a unit.
  do:
    - debug: msg="run a task"

    - debug: msg="run another task"
  when: condition

Spiritually block is an inline import, do is an inline include.