Deprecates utils.create_dir().

This function was a workaround for the exist_ok flag missing
from Python3.4. Now that Python3.4 is past the final release,
we no longer need to support that version.

Also fixes UTs broken by aosp/1231574.

Bug: None
Test: UTs.
Change-Id: If0592017e1bf374d6b4f5d27c17c32276979029a
diff --git a/acts/tests/google/wifi/WifiSensitivityTest.py b/acts/tests/google/wifi/WifiSensitivityTest.py
index 0afc214..5cd678d 100644
--- a/acts/tests/google/wifi/WifiSensitivityTest.py
+++ b/acts/tests/google/wifi/WifiSensitivityTest.py
@@ -155,7 +155,7 @@
         self.log.info('Access Point Configuration: {}'.format(
             self.access_point.ap_settings))
         self.log_path = os.path.join(logging.log_path, 'results')
-        utils.create_dir(self.log_path)
+        os.makedirs(self.log_path, exist_ok=True)
         if not hasattr(self, 'golden_files_list'):
             self.golden_files_list = [
                 os.path.join(self.testbed_params['golden_results_path'], file)