maas-clusterd must be restarted after installing python-vmomi

In order to probe-and-enlist VMware, we must install the python-pyvmomi package.

However, if it is not initially installed, and then added later, the probe-and-enlist still fails:

root@maastest-1404:/var/log/maas# dpkg --get-selections | grep vmomi
python-pyvmomi install

root@maastest-1404:/var/log/maas# tail maas.log | grep VMware
May 29 12:41:44 maastest-1404 maas.rpc.cluster: [ERROR] Failed to probe and enlist VMware nodes: Could not find a suitable VMware API (install python-pyvmomi)

If you then restart maas-clusterd, it works as expected after that.

root@maastest-1404:/var/log/maas# service maas-clusterd restart
maas-clusterd stop/waiting
maas-clusterd start/running, process 17625

It would be nice if, after installing the required package, it "just works".