Remove mox from tests/unit/virt/test_imagecache.py
Remove mox from tests/unit/virt/test_imagecache.py

This patch replaces mox with mock in
tests/unit/virt/test_imagecache.py.

Part of blueprint remove-mox-newton

Change-Id: Ia1db65f912bdff10c53add0b93cb01516ead9c54

gooddata/openstack-nova,vmturbo/nova,jianghuaw/nova,cloudbase/nova,Juniper/nova,rahulunair/nova,gooddata/openstack-nova,klmitch/nova,hanlind/nova,phenoxim/nova,mikalstill/nova,jianghuaw/nova,mahak/nova,Juniper/nova,hanlind/nova,jianghuaw/nova,rajalokan/nova,sebrandon1/nova,klmitch/nova,alaski/nova,rajalokan/nova,klmitch/nova,rajalokan/nova,mikalstill/nova,rahulunair/nova,klmitch/nova,openstack/nova,vmturbo/nova,gooddata/openstack-nova,phenoxim/nova,openstack/nova,cloudbase/nova,Juniper/nova,vmturbo/nova,openstack/nova,gooddata/openstack-nova,mikalstill/nova,hanlind/nova,rahulunair/nova,cloudbase/nova,rajalokan/nova,vmturbo/nova,mahak/nova,Juniper/nova,sebrandon1/nova,mahak/nova,alaski/nova,sebrandon1/nova,jianghuaw/nova