remove_superfluous_genids: more readable, better logging

Signed-off-by: Mike McClurg <mike.mcclurg@citrix.com>
CA-104674: Allow dbsync genid removal to be disabled

We copy the switched_sync function from dbsync_slave to allow the genid removal
code to be disabled on a pool-wide basis. To disable this behaviour, do:

xe pool-param-set uuid=${pool_uuid} other-config:genid=nosync

Signed-off-by: Mike McClurg <mike.mcclurg@citrix.com>