Cause copy module to fail on empty string as source (#27975)

* Fail if an empty string is set as src for copy module

Fixes #27363

* Cleanup task formatting on copy tests

Use multi-line YAML
Add debug statements with verbosity: 1 rather than leave them in there commented out.

* Add test for empty string as source

* Do more checks in order to add more specific errors messages

Add more integration tests for the various failure scenarios.
Cleanup some syntax on existing integration test tasks.

test/integration/targets/copy/tasks/main.yml

@@ -10,7 +10,7 @@
         # output_dir is hardcoded in test/runner/lib/executor.py and created there
         remote_dir: '{{ output_dir }}'
 
-    - name: create remote unprivileged remote user
+    - name: Create remote unprivileged remote user
       user:
         name: '{{ remote_unprivileged_user }}'
       register: user
@@ -21,7 +21,7 @@
         state: directory
         mode: 0700
 
-    - name: 'duplicate authorized_keys'
+    - name: Duplicate authorized_keys
       copy:
         src: $HOME/.ssh/authorized_keys
         dest: '{{ user.home }}/.ssh/authorized_keys'
@@ -46,7 +46,7 @@
         state: absent
       connection: local
 
-    - name: remote unprivileged remote user
+    - name: Remote unprivileged remote user
       user:
         name: '{{ remote_unprivileged_user }}'
         state: absent