Pass Message object to webob exception

Provide the Message object within Glance exception to webob exception
instead of try to convert it to a string. Because Message objects could
not be converted by str() since they may contain non-ascii characters.

Closes-Bug: #1292782
Related-Id: I352cda57fe119022c59c6c813b5c8053765b2d3c
Change-Id: I22b9123d8b3fe58d7dbd8fcde5a8dd58000e2da4
Signed-off-by: Zhi Yan Liu <zhiyanl@cn.ibm.com>
Merge "Pass Message object to webob exception"