core: NPE when getVMFullList returns no vm information

When getVMFullList fetches no information the code fails with NPE.

Bug-Url: https://bugzilla.redhat.com/1135959
Change-Id: Ifa1971f1181489e50877d080aec36ebc6d715f74
Signed-off-by: pkliczewski <piotr.kliczewski@gmail.com>