Fix various deprecation warnings for raw strings. (#585)

diff --git a/mobly/logger.py b/mobly/logger.py
index f82e94f..fba6b2d 100644
--- a/mobly/logger.py
+++ b/mobly/logger.py
@@ -29,7 +29,7 @@
 log_line_time_format = '%m-%d %H:%M:%S'
 log_line_timestamp_len = 18
 
-logline_timestamp_re = re.compile('\d\d-\d\d \d\d:\d\d:\d\d.\d\d\d')
+logline_timestamp_re = re.compile(r'\d\d-\d\d \d\d:\d\d:\d\d.\d\d\d')
 
 
 def _parse_logline_timestamp(t):
diff --git a/tests/mobly/controllers/android_device_test.py b/tests/mobly/controllers/android_device_test.py
index 22944aa..c8c42d6 100755
--- a/tests/mobly/controllers/android_device_test.py
+++ b/tests/mobly/controllers/android_device_test.py
@@ -188,7 +188,7 @@
     def test_get_device_too_many_matches(self):
         ads = mock_android_device.get_mock_ads(5)
         target_serial = ads[1].serial = ads[0].serial
-        expected_msg = "More than one device matched: \['0', '0'\]"
+        expected_msg = r"More than one device matched: \['0', '0'\]"
         with self.assertRaisesRegex(android_device.Error, expected_msg):
             android_device.get_device(ads, serial=target_serial)
 
diff --git a/tests/mobly/logger_test.py b/tests/mobly/logger_test.py
index 1ac9f1d..f1326f0 100755
--- a/tests/mobly/logger_test.py
+++ b/tests/mobly/logger_test.py
@@ -27,6 +27,18 @@
             1469134262116, time_zone=pytz.utc)
         self.assertEqual("07-21 20:51:02.116", actual_stamp)
 
+    def test_is_valid_logline_timestamp(self):
+        self.assertTrue(
+            logger.is_valid_logline_timestamp("06-21 17:44:42.336"))
+
+    def test_is_valid_logline_timestamp_when_wrong_lenght(self):
+        self.assertFalse(
+            logger.is_valid_logline_timestamp("  06-21 17:44:42.336"))
+
+    def test_is_valid_logline_timestamp_when_invalid_content(self):
+        self.assertFalse(
+            logger.is_valid_logline_timestamp("------------------"))
+
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/tests/mobly/test_runner_test.py b/tests/mobly/test_runner_test.py
index 26af2ee..6806f94 100755
--- a/tests/mobly/test_runner_test.py
+++ b/tests/mobly/test_runner_test.py
@@ -259,8 +259,8 @@
         tr = test_runner.TestRunner(self.log_dir, self.test_bed_name)
         with self.assertRaisesRegex(
                 test_runner.Error,
-                'TestRunner\._teardown_logger\(\) called before '
-                'TestRunner\.setup_logger\(\)!'):
+                r'TestRunner\._teardown_logger\(\) called before '
+                r'TestRunner\.setup_logger\(\)!'):
             tr._teardown_logger()
 
     def test_run_no_tests(self):