Reduce duplication of work in rpc.Client
Reduce duplication of work in rpc.Client

This patch removes the duplicate serialization and calls to
utils.GetNodeDaemonPort in rpc.Client, and instead moves them to calling
functions (the _*NodeCall ones recently introduced).

Reviewed-by: ultrotter

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