Fixes image create utf-8 multibyte test

Fixes test_create_image_specify_multibyte_character_image_name
so that it actually sends a UTF-8 multibyte character rather
than unicode. Also changes it to a 3 byte multibyte character
rather than a 4 byte multibyte character because glance currently
doesn't handle 4 byte utf-8 and will 500.

Change-Id: I064b563024a090899a4adcbbd462a18c5450830c
Related-Bug: 1006725
Merge "Fixes image create utf-8 multibyte test"