Add amqp=WARN,qpid=WARN to default_log_levels

The default value of default_log_levels includes amqplib=WARN.  However,
the kombu library uses an amqplib fork, amqp.  We were just recently
talking about how much of the debug log is full of amqp entries here:

http://lists.openstack.org/pipermail/openstack-dev/2013-October/017379.html

so just suppress them by default, because most of the time, they are not
needed.

In passing, add qpid=WARN for the same reason.  Alphabetize the list,
too, just because I felt like it.

Change-Id: Ie7590ac1033adaadade799da2588f566110efddc