add --allow-change-held-packages

this is needed if a package is listed as to be installed and to be removed
e.g.: ubuntu-server ubuntu-server-

bin/install_packages

@@ -60,7 +60,7 @@ my %classisdef;
 my $maxpl;  # maximum length of package list
 my @known;   # list of all known packages
 my $execerrors; # counts execution errors
-my $aptopt='-y -o Dpkg::Options::=--force-confdef -o Dpkg::Options::=--force-confnew';
+my $aptopt='-y -o Dpkg::Options::=--force-confdef -o Dpkg::Options::=--force-confnew --allow-change-held-packages';
 my $pacmanopts=' --noconfirm ';
 my $downloaddir="/var/cache/apt/archives/partial/"; # where to download packages that gets only unpacked
 my $debsourcesdir='/var/lib/fai/packages';