Allow overriding the log level for ironicclient

oslo provides a 'default_log_levels' conf variable for overriding
logging levels for certain modules. This could be used to override
ironicclient's default logging level, however it requires re-setting
all of the log levels for oslo's defaults. This is rather inconvenient.

I think it makes sense to allow the ironic virt driver to have an easy
config option for this. When in debug mode, ironicclient logs every
single API call and response. In an environment with a lot of nodes,
it clutters the logs.

This adds a 'client_log_level' config option to the 'ironic' config
section in nova. If it's unset (default), there's no change in behavior.
If it's set, it takes precedence over the 'default_log_levels',
'verbose', and 'debug' settings that one may have in nova.conf

Example usage:
[ironic]
client_log_level=INFO

DocImpact

Closes-bug: 1325663

Change-Id: Id16d5017e1d9ae5d2b15ff3daca177ab36a32869
Merge "Allow overriding the log level for ironicclient"