fix PEP8 W605 invalid escape sequence

Python 3.7 will get a lot stricter with escape sequences.  They must be
valid.

* https://lintlyci.github.io/Flake8Rules/rules/W605.html
* https://docs.python.org/3/whatsnew/3.6.html#deprecated-python-behavior

tests/build.TestCase

@@ -61,13 +61,13 @@ class BuildTest(unittest.TestCase):
                         os.path.join(testdir, 'source-files'))
         teststring = 'FAKE_VERSION_FOR_TESTING'
         fdroidserver.build.force_gradle_build_tools(testdir, teststring)
-        pattern = re.compile(bytes("buildToolsVersion[\s=]+'%s'\s+" % teststring, 'utf8'))
+        pattern = re.compile(r"buildToolsVersion[\s=]+'%s'\s+" % teststring)
         for p in ('source-files/fdroid/fdroidclient/build.gradle',
                   'source-files/Zillode/syncthing-silk/build.gradle',
                   'source-files/open-keychain/open-keychain/build.gradle',
                   'source-files/osmandapp/osmand/build.gradle',
                   'source-files/open-keychain/open-keychain/OpenKeychain/build.gradle'):
-            with open(os.path.join(testdir, p), 'rb') as f:
+            with open(os.path.join(testdir, p), 'r') as f:
                 filedata = f.read()
             self.assertIsNotNone(pattern.search(filedata))
 

tests/common.TestCase

@@ -204,7 +204,7 @@ class CommonTest(unittest.TestCase):
 
         with open(os.path.join(fdroidclient_testdir, 'build.gradle'), 'r') as f:
             filedata = f.read()
-        self.assertIsNotNone(re.search("\s+compileSdkVersion %s\s+" % testint, filedata))
+        self.assertIsNotNone(re.search(r"\s+compileSdkVersion %s\s+" % testint, filedata))
 
         with open(os.path.join(fdroidclient_testdir, 'AndroidManifest.xml')) as f:
             filedata = f.read()

tests/index.TestCase

@@ -53,9 +53,9 @@ class IndexTest(unittest.TestCase):
             _, fingerprint = fdroidserver.index.get_public_key_from_jar(jar)
             # comparing fingerprints should be sufficient
             if f == 'testy.jar':
-                self.assertTrue(fingerprint ==
-                                '818E469465F96B704E27BE2FEE4C63AB' +
-                                '9F83DDF30E7A34C7371A4728D83B0BC1')
+                self.assertEqual(fingerprint,
+                                 '818E469465F96B704E27BE2FEE4C63AB'
+                                 + '9F83DDF30E7A34C7371A4728D83B0BC1')
             if f == 'guardianproject.jar':
                 self.assertTrue(fingerprint == GP_FINGERPRINT)