Fix broken www-authenticate functional test

testQuotedWWWAuthenticateHeader functional test started failing
due to a change to keystonemiddleware.auth_token, which now adds
its own www-authenticate header in addition to the one that swift
keystoneauth adds.

This patch changes the functional test to check expected
swift generated header value is in the concatenation of
www-authenticate values.

Verified that functional tests still pass using tempauth.

Closes-Bug: 1368048
Change-Id: I913af077df800a559d259c1622f286ad10eae9df