jqueue: Implement {Add,Remove}Node
jqueue: Implement {Add,Remove}Node

These functions will be used to notify the queue about newly added
or removed nodes.

Reviewed-by: iustinp


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