Improve lock_path help and documentation

Improve help string to state default value and that it's mandatory.
Document set_defaults function.

DocImpact: Document that the value needs to evaluate to a valid path.
So, either environment variable is set or option is set.

Change-Id: I481d2f8107476ba166a18bc56d3b4c1be5ff726f
Merge fileutils from oslo-incubator

We need to get rid of our copy of log.py in oslo.concurrency.

oslo.concurrency code needs fileutils from oslo-incubator.
fileutils needs the common copy of log.py. What happens when we
import oslo.concurrency into nova, we end up with duplicate
options for default_log_levels. So to unravel the knots,
we switch fileutils over to python logging and hence remove
the need for common copy of log.py in oslo.concurrency.

Fixed the import for excutils as well since that change
has already been made in the oslo-incubator copy of fileutils

Closes-Bug: #1385492
Change-Id: I5310bf8a6584ac4f71b607d30b9dae0b12441d41
Remove unused incubator modules

All of these modules have been obsoleted by libs, so we don't need
them in this project anymore.

Change-Id: I99a52cb0f8f760ee54b6e6230dd83c9627d5cb46
Merge "Improve lock_path help and documentation"