Verify: Add and populate node_info dict

During information gathering we collect information from call_node_info, and
then when we cycle trough the nodes add it into a node_info dict containing a
node's free memory and disk. This will be useful later to verify that the
cluster is N+1 redundant. The disk space is saved as well because it can be
useful for checks about disk space redundancy.

Reviewed-by: iustinp