Handle VolumeBDMPathNotFound in _get_disk_over_committed_size_total

This handles the VolumeBDMPathNotFound error bubbling up from
_get_instance_disk_info during the update_available_resource periodic
task.

Related-Bug: #1371677

Change-Id: I10c20f3f5f96003fe69fcdc9133c661e6dc009b4
Merge "Handle VolumeBDMPathNotFound in _get_disk_over_committed_size_total"