Release resources that are allocated while configuring the connection to
the cluster. rados_shutdown() should only be needed after a successful
call to rados_connect(), however if the connection has been configured
with non-default parameters, some of the parameters may be allocated
before connecting. rados_shutdown() will free the allocated resources,
even if there has not been a connection yet.
Note that the finalizers get executed during garbage collection, which
can be forced by calling runtime.GC() for testing.
Fixes: #109
Signed-off-by: Niels de Vos <ndevos@redhat.com>