tests:integration: Fix warning about 01-main.yaml permissions

Avoid warnings like this across the test suite:

** (process:7269): WARNING **: 09:18:54.621: Permissions for /etc/netplan/01-main.yaml are too open. Netplan configuration should NOT be accessible by others.

tests/integration/base.py

@@ -34,6 +34,7 @@
 import tempfile
 import time
 import unittest
+import pathlib
 
 import gi
 
@@ -209,6 +210,9 @@ def setUp(self):
         self.workdir = self.workdir_obj.name
         self.config = '/etc/netplan/01-main.yaml'
         os.makedirs('/etc/netplan', exist_ok=True)
+        # prepare common config file with proper permissions
+        pathlib.Path(self.config).touch()
+        os.chmod(self.config, 0o600)
 
         # create static entropy file to avoid draining/blocking on /dev/random
         self.entropy_file = os.path.join(self.workdir, 'entropy')

tests/integration/regressions.py

@@ -88,7 +88,6 @@ def test_try_accept_lp1949095(self):
             f.write('''network:
   renderer: %(r)s
   version: 2''' % {'r': self.backend})
-            os.chmod(self.config, mode=0o600)
         p = subprocess.Popen(['netplan', 'try'], bufsize=1, text=True,
                              stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
         time.sleep(2)
@@ -103,7 +102,6 @@ def test_try_reject_lp1949095(self):
             f.write('''network:
   renderer: %(r)s
   version: 2''' % {'r': self.backend})
-            os.chmod(self.config, mode=0o600)
         p = subprocess.Popen(['netplan', 'try'], bufsize=1, text=True,
                              stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
         time.sleep(2)
@@ -151,7 +149,6 @@ def test_try_accept_lp1959570(self):
     br54:
       addresses:
       - "10.0.0.20/24"''' % {'r': self.backend})
-            os.chmod(self.config, mode=0o600)
         del os.environ['PATH']  # clear PATH, to test for LP: #1959570
         p = subprocess.Popen(['/usr/sbin/netplan', 'try'], bufsize=1, text=True,
                              stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)