This was required for a specific use case during pre-release
development and is no longer needed now the physical streaming
replication handling is implemented.
get_new_primary() returns NULL if no notification for the new primary has
been received, but the code was expecting it to return UNKNOWN_NODE_ID,
which was causing repmgrd to prematurely drop out of the new primary
detection loop if no notification had been received by the time the loop
started.
Also store the electoral term as a single row, single column table,
to ensure that all repmgrds see the same turn. It is then bumped
by the winning node after it gets promoted.
Various logging improvements.
The node(s) with higher ID will "yield", leaving the decision making
up to the node with the lower ID.
This happens very rarely, usually when the random delay is close
enough on two or mode nodes that vote initiation is simultaneous.
This will cover both the case when an entire node including
repmgrd goes down, and when one PostgreSQL instance goes down
but repmgrd is still up (in which case only one of the repmgrds
will handle the failover).
