RequestTimeoutException after ~250s after brief isolation

The robot symptom is basically the same as in CONTROLLER-1723 but the test scenario is different, so this is perhaps a different bug, especially when the suite when CONTROLLER-1723 appeared first is now passing.

This suite starts transaction writer (duration 180 seconds) on each member, then isolates the leader for 40 seconds, the rejoins it again. It is expected each writer finishes successfully. Two days ago two writers were passing, one failed on CONTROLLER-1708. Yesterday (two releng runs) this bug appeared alongside CONTROLLER-1708, and today only this symptom is there [0]. Two writers failed (161s ans 181s reported), one passed (the one on the new leader), not sure how reliable that is.

Sandbox run with verbose log also sees [1] this bug.

[0] https://logs.opendaylight.org/releng/jenkins092/controller-csit-3node-clustering-only-carbon/767/log.html.gz#s1-s28-t1-k2-k25-k1-k1
[1] https://logs.opendaylight.org/sandbox/jenkins091/controller-csit-3node-clustering-li-only-carbon/17/log.html.gz#s1-s2-t1-k2-k25-k1-k1