* Replace glance.common.utils.exception_to_str() with
oslo_utils.encodeutils.exception_to_unicode().
* Remove exception_to_str() from glance.common.utils
* Add "from oslo_utils import encodeutils" and remove "from
glance.common import utils" (when utils is no more used)
* glance/api/v2/images.py: replace utils.exception_to_str() with
six.text_type() to cast the oslo_i18n message to Unicode
Glance exception_to_str() function was not compatible with Python 3,
whereas exception_to_unicode() is compatible with Python 3, it's in Oslo
common libraries and it's well tested.
This patch was first generated by a tool (modified version of sixer),
and then fixed to respect the PEP8 (especially the constraint of 80
columns).
Change-Id: I86008c8adc0c5664f96573c1015cc15e2d06e3e2
1c186e23fd