Accurate exception info in api layer for aggregate

Adjust log information for exceptions in api layer for aggregate
according to
https://wiki.openstack.org/wiki/LoggingStandards#INFO_log_level_is_for_Operators
the LOG.info was removed because nova api already reported error to operator

Change-Id: I89394407495cf2d346e1f532ada236a4364aab24
Remove a not used function _get_ip_by_id

There is a not used function in floating_ips.py, Remove it
since no one use it.

Change-Id: I6a45c73d9e2a897fdc45f00e7363db204663cd3c
Be explicit about objects in _shutdown_instance()

This adds a docstring to _shutdown_instance() making it clear that
it takes an Instance object. Also, pass an object to the method
from the test.

Related to blueprint compute-manager-objects-juno

Change-Id: Ia80c82ca0f5d8a470bb8f01f1520a82748a4f877
Merge "Remove a not used function _get_ip_by_id"
Merge "Be explicit about objects in _shutdown_instance()"
Merge "Accurate exception info in api layer for aggregate"