status of create/drop node(group)

status:
create/drop nodegroup now works with one noticeable exception
replication cant be connected while the nodegroup is added.
i'll try to find time to fix this next week.

howto:
- start a 2 node cluster
- create table T1
- stop ndb_mgmd, add 2 nodes, start ndb_mgmd
- either stop the 2 running nodes and restart all 4
or rolling restart the 2 running nodes, and then start the 2 new nodes
- ndb_mgm> create nodegroup n1,n2
- alter table T1 add partitions partitions 2

Tata! fully online scaling of the cluster

howto backwards:
- drop table T1
- ndb_mgm> drop nodegroup X
- ndb_mgm> n1,n2 stop -a
- stop ndb_mgmd, remove the 2 nodes, start ndb_mgmd
- either stop the 2 running nodes and restart them
or rolling restart them

(A nodegroup is allowed to be dropped if it does not contain any data)

side effect:
- I added the possibility to specify nodegroups per node in the config-file
(this I intend to use for testing, but maybe someone might find it interesting)

future:
- magnus is working on "online configuration change" in the ndb_mgmd
once this is complete/functional, we can add the "add node"-command
so that the entire procedure can be done wo/ node restarts.

---