tests/functional/x86_64: Use the right Python interpreter & fix format string

The bad_vmstate test currently fails if the host does not have a "python3"
binary in $PATH because the vmstate-static-checker.py script is executed
directly, so that it gets run via its shebang line. Use the right Python
interpreter from sys.executable to fix this problem.

Additionally, there was another bug with the formatting of the error
message in case of failures: The "+" operator can only concatenate strings,
but not strings with integers. Use a proper format string here instead.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Acked-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20260114101101.36225-1-thuth@redhat.com>

tests/functional/x86_64/test_bad_vmstate.py

@@ -5,6 +5,7 @@
 '''Test whether the vmstate-static-checker script detects problems correctly'''
 
 import subprocess
+import sys
 
 from qemu_test import QemuBaseTest
 
@@ -41,12 +42,13 @@ class BadVmStateTest(QemuBaseTest):
                                        'vmstate-static-checker.py')
 
         self.log.info('Comparing %s with %s', src_json, dst_json)
-        cp = subprocess.run([checkerscript, '-s', src_json, '-d', dst_json],
+        cp = subprocess.run([sys.executable, checkerscript,
+                             '-s', src_json, '-d', dst_json],
                             stdout=subprocess.PIPE,
                             stderr=subprocess.STDOUT,
                             text=True, check=False)
         if cp.returncode != 13:
-            self.fail('Unexpected return code of vmstate-static-checker: ' +
+            self.fail('Unexpected return code of vmstate-static-checker: %d' %
                       cp.returncode)
         if cp.stdout != EXPECTED_OUTPUT:
             self.log.info('vmstate-static-checker output:\n%s', cp.stdout)