Remove explicit frontend instance guid.

It will use one of the available frontends.
Allows to make it work on other SlapOS Masters.
KVM doesn't leak .npm in /opt/slapgrid anymore.
Change name of slave instance doing vnc frontend.

UX.

Conflicts:
	software/kvm/common.cfg
Fix kvm development profile, badly copypasted from slaprunner.
Provide default slave list if not specified.

i.e if there is no slave yet.
kvm frontend listen to ipv6 and ipv4

Conflicts:
	software/kvm/software.cfg
Fix bad merge in KVM.
Increase KVM VNC password length.