qtest/ide: Fix small memory leak

For libqos debugging purposes, it's nice to
be able to assert that tests and associated libraries
have no memory leaks. To that end, free up the
trivial cmdline leak.

The remaining leaks caused by pc_alloc_init are fixed
instead by my first-fit pc_alloc implementation already
on the qemu-devel mailing list.

Signed-off-by: John Snow <jsnow@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
