Remove check for leadership change

Remove check for leadership change

see [0] for more details, but the idea is that we
have some sporadic cases where the isolated node
will report a node unreachable while it's being
rejoined to the cluster which triggers a new leader
election. This unreachable node messages can be
expected if the timing of things is a certain way
so the new leader election is also expected. In
the spirit of creating stable CSIT results without
sporadic failures, we will remove this test case.

[0] https://jira.opendaylight.org/browse/CONTROLLER-1865

JIRA: CONTROLLER-1865
Change-Id: Ic5da2d0748915a36e11eaa841f4b2772ecf7540f
Signed-off-by: Jamo Luhrsen <jluhrsen@redhat.com>