For unclear reason we set group ownership for tftp and http directories
to libvirt. This patch fixes that and use STACK_USER group there.
Also Recently [0] infra start installing libvirt from UCA
repository. The groups change with newer libvirt. Older Ubuntu used
'libvirtd', but now uses libvirt like Debian.
Update our local check that is needed for ironic standalone installation.
[0] c9a9e415b9a955525a407b78650f93e9193c8117
Change-Id: I2e4633a258e5f8a6bd442797dd4cfbf4894c798b