CLOUDSTACK-7143: improve build.sh ergonomics
CLOUDSTACK-7143: improve build.sh ergonomics

Added a bunch of possible arguments / environment variables, see the new usage
function for details (or run ./build.sh help).

Creates a new template with a unique name on every invocation, resulting in a
new virtualbox instance with a unique name. This makes it possible to build
multiple boxes at the same time, in parallel (including for example on a
multiuser box), and reduces the chance of failed build results conflicting
with each other.

Inject the version given on the command line (if any) into the created image.

wido/cloudstack,GabrielBrascher/cloudstack,DaanHoogland/cloudstack,GabrielBrascher/cloudstack,wido/cloudstack,jcshen007/cloudstack,wido/cloudstack,wido/cloudstack,DaanHoogland/cloudstack,resmo/cloudstack,jcshen007/cloudstack,GabrielBrascher/cloudstack,DaanHoogland/cloudstack,resmo/cloudstack,wido/cloudstack,resmo/cloudstack,resmo/cloudstack,jcshen007/cloudstack,GabrielBrascher/cloudstack,wido/cloudstack,resmo/cloudstack,DaanHoogland/cloudstack,jcshen007/cloudstack,DaanHoogland/cloudstack,jcshen007/cloudstack,DaanHoogland/cloudstack,resmo/cloudstack,GabrielBrascher/cloudstack,jcshen007/cloudstack,DaanHoogland/cloudstack,wido/cloudstack,GabrielBrascher/cloudstack,resmo/cloudstack,GabrielBrascher/cloudstack,jcshen007/cloudstack