Remove deprecated interface.LuigiConfigParser

It's been depreceated for > 1 year.

Instead use luigi.configuration.LuigiConfigParser
Merge pull request #523 from Tarrasch/remove_configuration_LuigiConfigParser

Remove deprecated interface.LuigiConfigParser
Remove deprecated interface.get_config()

Been >1 year. Instead, use luigi.configuration.get_config()
Merge pull request #525 from Tarrasch/remove_deprecated_get_config

Remove deprecated interface.get_config()
Lessen verbosity of tests

The problem at hand is that the travis logs get truncated to 10'000
lines.  Even though you can download the whole log file, you still get
completely log blind due to the super-verbose output.

The reason we get so much output is because the python logging module
defaults to outputting to stderr which nosetests does not capture. We
want it to capture the output from the loggers, since you only care
about the output if the test fails.

My solution is nice in the sense that it doesn't touch the code at all.
Instead, we configure the logger through the built in way of doing
configuration files in luigi.

I ping @jcrobak since he added client.cfg in `.gitignore` in commit
c642a9ec. I found this use case for commiting client.cfg sensible.

The logging config file was inspired by
https://docs.python.org/2/howto/logging.html
Merge pull request #524 from Tarrasch/less_verbose_tests

Lessen verbosity of tests
Make streaming map-reduce use atomic move_dir

This is essentially using the code introduced in spotify/luigi#393,
solving the exact same issue described there.

Without this patch, the renaming is of LBYL nature, and you could end up
with moving a directory inside another instead of actually renaming a
directory.

So others don't fall into the same pitfall, I added a comment to the
rename and move function discouraging it to be used for directories.