Re: [Libguestfs] [PATCH] builder: various improvements to the documentation

- convert the Fedora 20 examples to Fedora 25 - convert the yum examples to dnf - convert the Debian 7 examples to Debian 8 - mention that --core updates all the installed packages, not "core" ones - convert i386 to i686 for the Fedora 32bit examples - mention that autogenerated root passwords are printed on stdout - mention --get-kernel is deprecated in favour of virt-get-kernel - update URL to the Puppet installation documentation - edit the repository index documentation to make it clearer non-compressed templates are supported - remove old wrong paragraph about customization specified in command line not processed in the same order - use --install instead of --run-command '$pkgmgr install ...' - other minor changes