CID-1233086: Fix potential NPE blowup in UserVmManagerImpl

Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>
CID-1233084: Fix NPE in persisting volume in VolumeApiServiceImpl

Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>