Improve robustness for unreachable nodes #2206
Before this change, some pages were not loading when at least one node in the cluster was unreachable. With this change, information from reachable nodes is shown. Additionally, an error similar to the 404 page was created, which shows failed requests for pages which do not make sense to show at all when a node is not reachable.
* Check for null values in response maps. * Fixing linter hints. * Make `SystemJobsComponent` resilient against unreachable nodes. * Showing error instead of spinners for overview of unreachable node. * Make logging page resilient against unreachable nodes. * Change a bit the wording of PageErrorOverview (cherry picked from commit a1dbc51)