Upgrade python features when switching to python 3

[alastair]

In

gaia/test/unittest/test_generateclasificationproject.py

Line 31 in 479a19b

tmp_dir = 'tmp/'

it would be great to use tempfile.TemporaryDirectory, but this is only supported in python 3. When we upgrade to python 3 we should go through and see if there are things that we can replace with new features.