[Android] Allow concurrent builds using make_apk.py

 - Set temp directory to a random value using tempfile.mkdtemp that enables
   multiple simultaneous builds to happen on the same system
 - Fixed icon_dict being "None" when manifest file passed in without any path

 Bug=XWALK-2650
 Bug=XWALK-2664
Merge pull request #2472 from bspencer/parallel-build-conflict

 [Android] Allow concurrent builds using make_apk.py