AMT power operations no username configureable

[Stefan Helmert]

Using AMT to check power and power up computer, MAAS does not allow to specify the username. It defaults to "admin".

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: maas 2.4.2-7034-g2f5deb8b8-0ubuntu1
ProcVersionSignature: Ubuntu 4.18.0-17.18~18.04.1-generic 4.18.20
Uname: Linux 4.18.0-17-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.6
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Sun Apr 14 13:56:39 2019
InstallationDate: Installed on 2019-04-06 (8 days ago)
InstallationMedia: Ubuntu 18.04.2 LTS "Bionic Beaver" - Release amd64 (20190210)
PackageArchitecture: all
SourcePackage: maas
UpgradeStatus: No upgrade log present (probably fresh install)