Restrict config replication to master candidates
Restrict config replication to master candidates

This patch restricts the config data replication to master candidates
only.

Reviewed-by: imsnah

leshchevds/ganeti,ganeti-github-testing/ganeti-test-1,bitemyapp/ganeti,apyrgio/ganeti,ganeti/ganeti,dimara/ganeti,bitemyapp/ganeti,andir/ganeti,dimara/ganeti,mbakke/ganeti,onponomarev/ganeti,andir/ganeti,yiannist/ganeti,mbakke/ganeti,yiannist/ganeti,apyrgio/ganeti,ganeti-github-testing/ganeti-test-1,leshchevds/ganeti,onponomarev/ganeti,yiannist/ganeti,apyrgio/snf-ganeti,ganeti/ganeti,leshchevds/ganeti,ganeti/ganeti,mbakke/ganeti,grnet/snf-ganeti,andir/ganeti,grnet/snf-ganeti,apyrgio/snf-ganeti