VMware: fix driver support for hypervisor uptime

This method was previously not implemented and would throw an exception
with the tempest tests. It will now redirect the administrator to access
the host to het the uptime.

Fixes bug 1199946

Change-Id: I073f50fee6aa76e912753c0754d632ff2adfa287
Merge "VMware: fix driver support for hypervisor uptime"