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

tests/vm/freebsd

@@ -20,6 +20,7 @@ class FreeBSDVM(basevm.BaseVM):
     name = "freebsd"
     BUILD_SCRIPT = """
         set -e;
+        rm -rf /var/tmp/qemu-test.*
         cd $(mktemp -d /var/tmp/qemu-test.XXXXXX);
         tar -xf /dev/vtbd1;
         ./configure {configure_opts};

tests/vm/netbsd

@@ -20,6 +20,7 @@ class NetBSDVM(basevm.BaseVM):
     name = "netbsd"
     BUILD_SCRIPT = """
         set -e;
+        rm -rf /var/tmp/qemu-test.*
         cd $(mktemp -d /var/tmp/qemu-test.XXXXXX);
         tar -xf /dev/rld1a;
         ./configure --python=python2.7 {configure_opts};

tests/vm/openbsd

@@ -20,6 +20,7 @@ class OpenBSDVM(basevm.BaseVM):
     name = "openbsd"
     BUILD_SCRIPT = """
         set -e;
+        rm -rf /var/tmp/qemu-test.*
         cd $(mktemp -d /var/tmp/qemu-test.XXXXXX);
         tar -xf /dev/rsd1c;
         ./configure --cc=x86_64-unknown-openbsd6.1-gcc-4.9.4 --python=python2.7 {configure_opts};