DiscoveryFailures can happen for a variety of reasons, ranging
from service misconfiguration to a keystone outage to a transient
network failure. If we don't catch and handle the failure here,
it will almost certainly cause something further up the WSGI stack
to send a 500 Internal Error (and likely log a traceback).
A log line like
Unable to validate token: Could not find versioned identity
endpoints when attempting to authenticate. Please check that
your auth_url is correct. Unable to establish connection to
http://keystone:35357: HTTPConnectionPool(host='keystone',
port=35357): Max retries exceeded with url: / (Caused by
NewConnectionError('<urllib3.connection.HTTPConnection
object at 0x7fc53e22e050>: Failed to establish a new
connection: [Errno 111] ECONNREFUSED',))
should be plenty enough for an operator to assess the situation;
I don't need a 29-frame traceback.
Change-Id: I946388c09b2ca0230d2cef009c679a7ac7c8398f
86904543eb