Minor fix in GPU test
Minor fix in GPU test

Adding sleep of 180 seconds after reboot, giving time to load nvidia drivers.

konkasoftci/azure-linux-automation,v-sirebb/azure-linux-automation,iamshital/azure-linux-automation,iamshital/azure-linux-automation,v-sirebb/azure-linux-automation,v-sirebb/azure-linux-automation,konkasoftci/azure-linux-automation,iamshital/azure-linux-automation,konkasoftci/azure-linux-automation