log: split log variables from root object

log: split log variables from root object

The original plan was to avoid any global variables in the library. Thus
the logging variables were tied to the root object which is available
via the fabric API.

The default NVME API doesn't have the root object thus we had to add a
global variable to set log level etc. But the API to set these variables
is done via the root object.

This approach enforces the caller side to create an default root object
to initialize the default logging level. This introduces unnecessary
complexity on the caller side and wastes resources.

Let's split the default logging setting from the root object.

Signed-off-by: Daniel Wagner <dwagner@suse.de>