Fix test failure if client.cfg defines a logging_conf_file.

When /etc/luigi/client.cfg had a logging_conf_file entry, like

    logging_conf_file = /etc/luigi/logging.ini

test_cmdline_logger would fail with something like

    AssertionError: [call(None)] != [call('/etc/luigi/logging.ini')]
Merge pull request #373 from anyman/master

Adding debug message when using the HDFS existence check
Remove --lock warning when it's not passed

Previously you would *always* get the deprecation warning. Regardless if
it was passed.

Note however that it still can have an effect to pass the flag.
Unfortunately, the hash of the lock-file is based on even the
non-semantical flags like --lock (I want to kill myself).
Choosing port and interface.
Merge pull request #375 from bearstech/host_and_port

Choosing port and interface.
Fixed issue introduced in #335

Forgot to add the RPC method, so workers would always fail invoking add_worker.

This was a pure cosmetic change that didn't lead to any deeper issues
Merge pull request #376 from erikbern/erikbern/fix-335

Fixed issue introduced in #335
Don't crash if loading a corrupt pickle state file

Previously the luigi server would crash on startup if the pickle file that stores its state is corrupt for some reason
Merge pull request #355 from spotify/freider/load_no_crash_rebased

Don't crash if loading a corrupt pickle state file
Merge pull request #374 from Tarrasch/remove-lock-warning

Remove --lock warning when it's not passed
Add event for broken task
Merge pull request #377 from rtshadow/broken_task_event

Add event for broken task
Provide dynamic loading of modules

This adds a new interface to Luigi that takes a module parameter on the command line

Eg. you can run
python something.py --module my_luigi_job FooTask --x 1 --y 2

Inspired by discussion in #365
Worker returns boolean value for add and run commands, depending on their outcome
Merge pull request #378 from spotify/erikbern/dynamic-module-loading

Provide dynamic loading of modules
Add a script to find all deps on the paths b/w task T and task S.
This is a practical way of finding all upstream tasks of task S
Merge pull request #365 from rantav/find-upstream-deps

Create a script to find upstream dependencies
More unit tests, interface.run returns success value
Merge pull request #379 from rtshadow/worker_returns_action_status

Worker returns action status
Merge pull request #371 from miku/test_cmdline_logger

Fix test failure if client.cfg defines a logging_conf_file.