[CA-139904] netsettings save & restore

Create new netsettings and qnetsettings executables for saving
  and restoring network settings

Add netsettings to the drivers msi

Save netsettings before installing via drivers msi

Installwizard restores netsettings after drivers installed

Installwizard restarts pv net devices to ensure new settings are accepted

Installwizard stores nsis settings in a form netsettings can read from

Installwizard works around xennet not installing when updated from a
  xenvif with no alias backing it up

Signed-off-by: Ben Chalmers <Ben.Chalmers@citrix.com>