Change how hspace reads cmdline args for std specs

For the standard specs, hspace currently takes separate options for
the memory, disk and VCPUs. For the tiered specs, which were
introduced later, it takes a single option with all three values
combined.

This patch adds a backward-incompatible change to the standard spec,
basically moving it to the same single option format, which is a bit
more simple (both in the code and on the command line). This is
"needed" for future changes, where the command line will just
overwrite what we get from cluster, instead of setting the starting
point.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>