New module postgresql_ping: Checks remote PostgreSQL server availability. (#51477)

* New module postgresql_ping: simple module to check remote PostgreSQL server availability.

* New module postgresql_ping: simple module to check remote PostgreSQL server availability, doc fixes

* postgresql_ping: added integration tests

* New module postgresql_ping: misc changes

* New module postgresql_ping: change return suit

* New module postgresql_ping: tests reformatting, return value

* Various cosmetic/documentation fixes

* A few more fixes

* And even more cleanups

* Fix PEP8 issue

test/integration/targets/postgresql/tasks/postgresql_ping.yml

@@ -0,0 +1,35 @@
+# Test code for the postgresql_ping module
+# Copyright: (c) 2019, Andrew Klychkov (@Andersson007) <aaklychkov@mail.ru>
+# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+
+- name: postgresql_ping - test return values
+  become_user: "{{ pg_user }}"
+  become: yes
+  postgresql_ping:
+    db: "{{ db_default }}"
+    login_user: "{{ pg_user }}"
+  register: result
+  ignore_errors: yes
+
+- assert:
+    that:
+      - result.is_available == true
+      - result.server_version != {}
+      - result.server_version.major != false
+      - result.server_version.minor != false
+      - result.changed == false
+
+- name: postgresql_ping - check ping of non-existing database doesn't return anything
+  become_user: "{{ pg_user }}"
+  become: yes
+  postgresql_ping:
+    db: "{{ db_name_nonexist }}"
+    login_user: "{{ pg_user }}"
+  register: result
+  ignore_errors: yes
+
+- assert:
+    that:
+      - result.is_available == false
+      - result.server_version == {}
+      - result.changed == false