wbatch: elevated privileges for create_hostnet

Currently, create_hostnet.bat asks no less than six times for elevated
privileges (once for each network created or modified). This change adds
code that allows create_hostnet to keep the elevated privileges while
configuring networks. That is, it prompts once rather than six times.

Partial-Bug: 1312764
Implements: blueprint openstack-training-labs
Change-Id: I30f9c158c674f1e308dc14d5e2efef184b6d464b
Merge "wbatch: elevated privileges for create_hostnet"