VCDriver - Ignore host in Maintenance mode in stats update

The VCDriver during stats update checks only for connected hosts.
However hosts which are in connected state to the Cluster can
be set to Maintenance mode.
The cluster does not boot instances to hosts which are in
maintenance mode.
Hence the VCDriver should check for hosts which are in
maintenance mode and ignore them for stats update.
VISDK API returns True for the property inMaintenanceMode for
Hosts which are in maintenance mode

Change-Id: Ieaf7530ed2d98c59c5450e8cb75e209823193d49
Closes-Bug: #1316674
Merge "VCDriver - Ignore host in Maintenance mode in stats update"