Medium: Tools: crm: drop empty attributes elements

The shell can handle empty attributes' sets, but can't digest the
whole object if they come along with another set of the same
kind. This patch makes crm drop all empty sets. Should there be
an outcry, we can make it drop only empty sets which come in
combination with non-empty ones.

Mercurial revision: e7b3a7327e2fbc6486edcab06baa1bf09f7b13bd