Add API that returns iSCSI Multipath status

[ahadas]

We want to monitor the iSCSI multipath status on our hosts.
So we notice it when for example 1 path is down to the iSCSI LUN.

oVirt notices this perfectly, as you can see this in the alerts/log:
2020-09-18 09:53:08,880+02 WARN [org.ovirt.engine.core.dal.dbbroker.auditloghandling.AuditLogDirector] (EE-ManagedScheduledExecutorService-engineScheduledThreadPool-Thread-86) [] EVENT_ID: FAULTY_MULTIPATHS_ON_HOST(11,500), Faulty multipath paths on host kvm001 on devices: [3600a0980383056645524502f414a726a]

The thing is, parsing the log and then alert something is not very useful sometimes.

Our use-case uses Nagios/Icinga(2) for example to monitor the oVirt setup.

Is would be great if the API was exended with a call that returns the iSCSI Multipath status on that host.

The following call gives iSCSI info now:
/ovirt-engine/api/hosts/xxxx/storage

It would be nice to extend this with available_paths: int for example.
Then if paths > available_paths -> trigger alert in our monitoring.

Original bug: https://bugzilla.redhat.com/show_bug.cgi?id=1880375