Add modification of the reserved logical volumes

This doesn't allow addition/removal of individual volumes, only
wholesale replace of the entire list. It can be improved later, if we
ever get generic container parameters.

The man page changes replaces some tabs with spaces (hence the
whitespace changes).

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