Use file logger for all command specific logs.
This patch also fixes some usage that doesn't
follow rules in:
http://docs.openstack.org/developer/oslo.i18n/guidelines.html
After this patch, all self.log and self.app.log
will be standardized to LOG().
NOTE: In shell.py, we got the log in class OpenStackShell,
which is also known as self.app.log in other classes.
This logger is used to record non-command-specific logs.
So we leave it as-is.
Change-Id: I114f73ee6c7e84593d71e724bc1ad00d343c1896
Implements: blueprint log-usage
047cb68493