tests: Don't touch original britney.conf

Don't change britney.conf from the source tree and restore it back after the
tests; this is prone to leave a broken config behind if a test gets
interrupted. Instead, copy the file to our temp dir, and let tests hack on it
there.

(Introduced in lp:~canonical-ci-engineering/britney/boottesting-support)

tests/__init__.py

@@ -133,18 +133,14 @@ class TestBase(unittest.TestCase):
         super(TestBase, self).setUp()
         self.data = TestData()
         self.britney = os.path.join(PROJECT_DIR, 'britney.py')
-        self.britney_conf = os.path.join(PROJECT_DIR, 'britney.conf')
+        # create temporary config so that tests can hack it
+        self.britney_conf = os.path.join(self.data.path, 'britney.conf')
+        shutil.copy(os.path.join(PROJECT_DIR, 'britney.conf'), self.britney_conf)
         assert os.path.exists(self.britney)
-        assert os.path.exists(self.britney_conf)
 
     def tearDown(self):
         del self.data
 
-    def restore_config(self, content):
-        """Helper for restoring configuration contents on cleanup."""
-        with open(self.britney_conf, 'w') as fp:
-            fp.write(content)
-
     def run_britney(self, args=[]):
         '''Run britney.
 

tests/test_autopkgtest.py

@@ -39,7 +39,6 @@ class TestAutoPkgTest(TestBase):
             'BOOTTEST_ENABLE   = yes', 'BOOTTEST_ENABLE   = no')
         with open(self.britney_conf, 'w') as fp:
             fp.write(new_config)
-        self.addCleanup(self.restore_config, original_config)
 
         # fake adt-britney script
         self.adt_britney = os.path.join(

tests/test_boottest.py

@@ -143,7 +143,6 @@ class TestBoottestEnd2End(TestBase):
             'BOOTTEST_FETCH    = yes', 'BOOTTEST_FETCH    = no')
         with open(self.britney_conf, 'w') as fp:
             fp.write(new_config)
-        self.addCleanup(self.restore_config, original_config)
 
         self.data.add('libc6', False, {'Architecture': 'armhf'}),