Replace oslo_utils.encodeutils.exception_to_unicode

The function is being deprecated now because it is equivalent to
str(ex) in Python 3.

Depends-on: https://review.opendev.org/c/openstack/oslo.utils/+/938929
Change-Id: I7c9ca3730e1ab6ffdaf8cb78c002ac4e157fe2f1

glanceclient/shell.py

@@ -660,4 +660,4 @@ def main():
     except Exception as e:
         if utils.debug_enabled(argv) is True:
             traceback.print_exc()
-        utils.exit(encodeutils.exception_to_unicode(e))
+        utils.exit(str(e))