This script is similar to build-capstan-img. Later we can hook this
script to scripts/build-osv-release to build images used without
capstan. It takes the same args with build-capstan-img.

Example output:

   $ find build/standalone
   build/standalone/cloudius/
   build/standalone/cloudius/osv-iperf
   build/standalone/cloudius/osv-iperf/osv-iperf.esx.ova
   build/standalone/cloudius/osv-iperf/osv-iperf.qemu.qcow2
   build/standalone/cloudius/osv-iperf/osv-iperf.vbox.ova
   build/standalone/cloudius/osv-iperf/osv-iperf.vmw.zip
   build/standalone/cloudius/osv-iperf/osv-iperf.gce.tar.gz

Signed-off-by: Asias He <asias@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>