ceph-iscsi does not provision additional gateway when a new unit of ceph-iscsi is deployed

[Przemyslaw Hausman]

Consider the following scenario.

Two ceph-iscsi units are deployed. The machine hosting one unit irreversibly fails and has to be replaced. The unit is lost.

Now we want to provision additional ceph-iscsi unit to fill in for the lost one.

From the user perspective I'd expect that the charm automatically handles adding a new node as a gateway.

Currently it does not happen. The operator must run manual actions with `gwcli` utility to remove failed gateway and add the new one:

sudo gwcli

/> cd iscsi-targets/iqn.2003-01.com.ubuntu.iscsi-gw:iscsi-igw/gateways/

/iscsi-target...-igw/gateways> ls
o- gateways ............................... [Up: 1/2, Portals: 2]
  o- node02.maas ............................ [172.27.81.85 (UP)]
  o- node03.maas ........................[172.27.81.86 (UNKNOWN)]

/iscsi-target...-igw/gateways> delete node03.maas confirm=true
Deleting gateway, node03.maas

/iscsi-target...-igw/gateways> create node10.maas 172.27.81.94 skipchecks=true
OS version/package checks have been bypassed
Adding gateway, sync'ing 1 disk(s) and 1 client(s)

All gateways accessible
ok