Running 'make -C tests check TESTS=qemuagenttest' left a directory
/tmp/libvirt_XXXXXX/ behind.  The culprit was failure to cleanup
when short-circuiting an expensive test.

* tests/qemuagenttest.c (testQemuAgentTimeout): Free resources
when skipping expensive test.
Signed-off-by: NEric Blake <eblake@redhat.com>