tests/vm: Clean out old working directories on build

When we do a build inside one of the BSD VMs, first
delete any stale old build directories from the VM's
/var/tmp. This prevents the VM from running out of
disk space after it has been used for a dozen or
so builds.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-id: 20180820124811.7982-1-peter.maydell@linaro.org
3 files changed