Added arg and if statement prevents db_sync from being run where db service is not active i.e. the compute
Add charset param to nova::db::mysql

Allow to specify the database charset but still default to 'latin1' if
none is provided.

Remove nova::params::nova_db_charset. Both osfamily were using 'latin1'
since the update for Folsom in 76d4632.
Change rabbit_host/rabbit_port to rabbit_hosts array

This enable the 'rabbit_ha_queues' when many rabbit_hosts is present