fix tests that fail to close files that they open

[ctb]

There are several tests in test_lca.py that are causing warnings during the tests, because I did a bad thing and opened files without closing them.

The three tests are:

test_single_summarize_to_output
test_single_classify_to_output
test_single_classify_to_output_no_name

and they all use some variant of this code,

outdata = open(os.path.join(location, 'outfile.txt'), 'rt').read()

which doesn't close the file. This results in a warning when py.test runs the tests.

The proper usage is something like

with open(...) as fp:
   outdata = fp.read()

which will use a context manager to close the file after the with block.

Fix!

[keyabarve]

Can I try to fix this? @ctb

[ctb]

sure!