Aligning python signature with os-autoinst limitations

Python test modules do not support any other argument but `self`.

This limitation is enforced now in os-autoinst and now documented
in the docs.

docs/WritingTests.asciidoc

@@ -65,7 +65,7 @@ And here is an example in Python:
 -------------------------------------------------------------------
 from testapi import *
 
-def run(*_):
+def run(self):
     # write in this block the code for your test.
 -------------------------------------------------------------------
 
@@ -76,7 +76,7 @@ _Please note that the subroutine marked with `*1` are optional._
 [source,python]
 -------------------------------------------------------------------
 # Written in type-hinted python to indicate explicitly return types
-def run(*_):
+def run(self):
 def test_flags(): -> dict # *1
 def post_fail_hook(): -> None # *1
 def pre_run_hook(): -> None # *1
@@ -222,7 +222,7 @@ from testapi import *
 
 # [...] omitted for brevity
 
-def run(*_):
+def run(self):
     perl.require('x11utils')
 
     # Start vncviewer - notice the named arguments passed as positional arguments
@@ -235,10 +235,12 @@ def run(*_):
     # [...] omitted for brevity
 -------------------------------------------------------------------
 
-Additionally, the `run` method in Python is not able to handle any argument
-passed. Due to how `Inline::Python` handles arguments passing between Perl <->
-Python, references to complex Perl objects do not reach python properly and
-they can't be used.
+Additionally, Python tests do not support `run_args`. An error will be present
+when a python test detects the presence of `run_args` on schedule.
+
+This is because of the way `Inline::Python` handles arguments passing between
+Perl <-> Python, references to complex Perl objects do not reach python
+properly and they can't be used.
 
 === Example Perl test modules
 [id="testmodule_perl_examples"]
@@ -359,7 +361,7 @@ implementing the interface described above.
 --------------------------------------------------------------
 from testapi import *
 
-def run(*_):
+def run(self):
     assert_screen('openqa-logged-in')
     assert_and_click('openqa-search')
     type_string('shutdown.pm')