Add RPC call master_node_name
Add RPC call master_node_name

In Haskell, support the RPC call "master_node_name" by which a
node is asked who it believes is the master node. Luxid will need
this to carry out a voting.

Signed-off-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>
Reviewed-by: Petr Pudlak <9d19625f8ee825a2c398462ed335cbcf98f79c32@google.com>

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