HyperV Driver - Fix to implement hypervisor-uptime

The hyperv driver currently does not return the hypervisor-uptime.
This fix does the necessary changes to return the hypervisor-uptime.
The uptime returned is in similar format to libvirt driver uptime

The uptime is calculated using the windows function GetTickCount64
More details about this function available at
http://msdn.microsoft.com/en-us/library/windows/desktop/ms724411%28v=vs.85%29.aspx

The function GetTickCount64 returns in millisecs the time since the host
is up.

Change-Id: Ib3cd90b17f64e369badaddb764ac9e6b9f6c1a4b
Closes-Bug: #1335559
Merge "HyperV Driver - Fix to implement hypervisor-uptime"