simplify db replication stuff

[binary1230]

can probably further simplify db replication puppet:

1. remove difference between "normal mode" i.e. no replication and "master mode" i.e. listening for connections.

2. simplify config files, only difference between the slave and master mode is 'hot_standby': value => 'on';. move common stuff as the default config, and slave nodes only put hot_standby on.

3. probably drop recovery.conf in all stuff and write standby_mode always, primary_conninfo only if slave