Make invocation ID optional

[siegfriedweber]

Fixes #150

[razvan]

Update: please ignore. I used the wrong agent version.

I'm not sure if this PR should cover the entire pod lifecycle or just the kubectl logs usecase.

I get the following error on Centos 7 when creating a single node Zookeeper cluster:

Jun 04 09:09:05 1825a20b6a8e stackable-agent[86]: [2021-06-04T09:09:05Z ERROR stackable_agent::provider::states::pod::starting] Error receiving InvocationID of unit [default-zookeeper-simple-default-server-1825a20b6a8e-zookeeper.service]. org.freedesktop.DBus.Error.UnknownProperty: Unknown property or interface.
Jun 04 09:09:05 1825a20b6a8e stackable-agent[86]: [2021-06-04T09:09:05Z ERROR krator::state] Object state machine exited with error. error=Error receiving InvocationID of unit [default-zookeeper-simple-default-server-1825a20b6a8e-zookeeper.service]. org.freedesktop.DBus.Error.UnknownProperty: Unknown property or interface.

So I cannot test the logs call because the pod never reaches a running state.

[razvan]

Update: please ignore. I used the wrong agent version.

On Debian I don't see the featureLogs annotation of the pod:

Annotations:    <none>

But kubectl logs works.

[razvan]

Looks good.