proposal: deprecate always_run in favor of checkmode_run

docs/proposals/rename_always_run.md

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+# Rename always_run to checkmode_run
+
+*Author*: René Moser <@resmo>
+
+*Date*: 02/03/2016
+
+## Motivation
+
+The task argument `always_run` is misleading.
+
+Ansible is known to be readable by users without deep knowledge of creating playbooks, they do not understand
+what `always_run` does at the first glance.
+
+### Problems
+
+The following looks scary if you have no idea, what `always_run` does:
+
+```
+- shell: dangerous_cleanup.sh
+  when: cleanup == "yes"
+  always_run: yes
+```
+
+You have a conditional but also a word that says `always`. This is a conflict in terms of understanding.
+
+## Solution Proposal
+
+Deprecate `always_run` by rename it to `checkmode_run`:
+
+```
+- shell: dangerous_cleanup.sh
+  when: cleanup == "yes"
+  checkmode_run: yes
+```