If a lagged node is not aware of newly added node(s), it simply
cannot communicate with them. When it suspects its own eviction,
it inspects certificates in them, would find itself still among
consenter set. And if the leader happens to be among those new
nodes, we have a deadlock.

To break this, when a node suspects its own eviction, it also
triggers a catchup to actually pull blocks and commit them, so
that it can eventually recognizes new nodes.

Change-Id: Id2e9a423221e4a3bebeeeaf7da5f120396f342dd
Signed-off-by: Jay Guo <guojiannan1101@gmail.com>