Currently we configure and build under "$QEMU_SRC/tests/docker" which is
dubious. Create a fixed directory (to be friendly to ccache) and change
to there before calling build_qemu.
Signed-off-by: Fam Zheng <famz@redhat.com>
Message-Id: <1475047892-11955-1-git-send-email-famz@redhat.com>