Add support for specifying morefs in vsphere.conf

[SandeepPissay]

The current vsphere.conf file accepts names of virtual center inventory objects like datacenter, default datastore, folder etc. Even though these are user friendly, they are not as durable as moref IDs. The names of these inventory objects can be easily changed in vSphere client and when that happens this will break vsphere cloud provider.

So, I'm filing this issue to track the work involved to add support for specifying moref IDs in vsphere.conf in addition to specifying inventory names. Its better we have both ways and the users of vsphere cloud provider have an option to pick whichever they want(user friendly vs more durable moref IDs).

[SandeepPissay]

We should also handle the cases where we have multiple virtual center inventory objects with same name under the same datacenter. Example - we could have a cluster "cluster-1" under folder-1 and folder-2.