Supress client debug messages
Supress client debug messages

cliff sets log level to DEBUG in `run` function [1], need to overwrite
this configuration to depress DEBUG messages. This patch adds such
configuration in `prepare_to_run_command` function which will be called
by cliff after it sets log level to DEBUG [2][3].

[1] https://github.com/openstack/cliff/blob/master/cliff/app.py#L248
[2] https://github.com/openstack/cliff/blob/master/cliff/app.py#L279
[3] https://github.com/openstack/cliff/blob/master/cliff/app.py#L393

Change-Id: I5c270d74cb09e90b8a98fd8febf587b98db2306f
Closes-bug: #1681966

openstack/python-barbicanclient