libqos: split qos-test and libqos makefile vars

libqos: split qos-test and libqos makefile vars

Most qos-related objects were specified in the qos-test-obj-y variable.
qos-test-obj-y also included qos-test.o which defines a main().
This made it difficult to repurpose qos-test-obj-y to link anything
beside tests/qos-test against libqos. This change separates objects that
are libqos-specific and ones that are qos-test specific into different
variables.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200220041118.23264-11-alxndr@bu.edu
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>