Handle node details load failure gracefully on UI

Closes #4511 and #4552

See merge request gitlab-org/gitlab-ee!3992

(cherry picked from commit 2865c0ba)

68658bf4 Update classes for node status icon
0b34ccbd Emit `nodeDetailsLoadFailed` event on node details load failure
e8453efe Update test for node details load failure
6cf58a22 Handle node details load failure
589cfc25 Update tests for node details load failure
1c30818f Add changelog entry
78e83eb1 Default value to `0` when it is `null`
edaecca7 Update prop name