base: show size as %zu instead %zd

For big numbers otherwise negative sizes for memory chunks are displayed.

Issue #1011
base: catch errors during ram_ds allocation

Issue #1011
nova: throw exception if ram_ds setup fails

Fail hard if no large enough virtual memory area can be found where to map
the memory from the kernel to core.

Additionally clear dataspaces in junks if it can't be done in one large junk.

Fixes #1011