Fix test_quota.py on Python 3

Exception.message attribute has been removed in Python 3.

Change-Id: Icd733b9912598294c30ae2a6602627f1e68a2e3c
Python3: pass bytes as 'contents' to create_tempfiles()

os.write() expect bytes, so make sure that's what we're passing.

Change-Id: I98eae905e1d2b3802b7f5326c40f8b66aba21519
Merge "Python3: pass bytes as 'contents' to create_tempfiles()"
Merge "Fix test_quota.py on Python 3"