Update log level of session related logs
Update log level of session related logs

In api, session recreation log messages are at WARN level which
can confuse administrators. These messages indicate nothing
unusual and should be at debug level.  VIM error while checking
active session within an expired session is also normal and
shouldn't raise a warning.

This patch fixes the log level of these messages.

Change-Id: Ia5f81c20890973888f90a99e87e71cd18e8dd24b

openstack/oslo.vmware