Pass tenant_name to zuul config.

Turns out that while keystoneclient does not require a tenant_name be
set swiftclient does require it so the fix to not pass a tenant_name to
zuul did not work.

Alex_Gaynor pointed out the reason using the normal tenant_name doesn't
work with Rax object store is that the tenant_name for object store in
Rax is different than the normal tenant_name. Use that different and
correct tenant_name instead.

Change-Id: I13d6b8dfc190d35178e7fc979d7feb58e7e1f8dd
Merge "Pass tenant_name to zuul config."