Left UI available if GET /api/nodes returns 500th

Refers to https://mirantis.jira.com/browse/PRD-1109 (Need to remove GET /api/nodes request from Clusters page) issue.
Specific failure callback will be added within https://mirantis.jira.com/browse/PRD-1142 (Failure callbacks for all UI requests) task.

Also https://mirantis.jira.com/browse/PRD-887 (Can't select an interface info text on node's Configure Networks dialog) issue is fixed.