VNET for ARM changes.
VNET for ARM changes.

1. Updated default username used in tests. ("test" user is not supported
in ARM mode)
2. Added Virtual Network Basic information in XML file.
3. Updated VNET test definitions.

Nidylei/azure-linux-automation,konkasoftci/azure-linux-automation,iamshital/azure-linux-automation,FreeBSDonHyper-V/azure-freebsd-automation,iamshital/azure-linux-automation,FreeBSDonHyper-V/azure-freebsd-automation,hglkrijger/azure-linux-automation,iamshital/azure-linux-automation,v-sirebb/azure-linux-automation,konkasoftci/azure-linux-automation,v-sirebb/azure-linux-automation,Nidylei/azure-linux-automation,FreeBSDonHyper-V/azure-freebsd-automation,hglkrijger/azure-linux-automation,v-sirebb/azure-linux-automation,Nidylei/azure-linux-automation,konkasoftci/azure-linux-automation,hglkrijger/azure-linux-automation