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/WifiIOTTwPkg1Test.py b/acts/tests/google/wifi/WifiIOTTwPkg1Test.py
index 359560d..c6f8c3d 100644
--- a/acts/tests/google/wifi/WifiIOTTwPkg1Test.py
+++ b/acts/tests/google/wifi/WifiIOTTwPkg1Test.py
@@ -78,7 +78,7 @@
 
         # create folder for IOT test result
         self.log_path = os.path.join(logging.log_path, "IOT_results")
-        utils.create_dir(self.log_path)
+        os.makedirs(self.log_path, exist_ok=True)
 
         Header=("test_name","throughput_TX","throughput_RX")
         self.csv_write(Header)