Use dnf to cleanup old kernels

As described in the comment, there is a dnf equivalent of this command
that doesn't require us installing yum-utils (which drags in yum on
dnf-only systems such as f23)

This is a small consequence to this -- due to us not installing
yum-utils some installs will now be completely yum free.  This causes
a breakage in ironic-agent 99-remove-extra-packages where we remove
the yum package.  There is a long-standing bug/feature where missing
packages in a group of packages do not cause yum/dnf to exit with
failure, but uninstalling a single package will.  Because we have made
the systems yum-free, the uninstall of yum can fail in this corner
case.

It has always been like this, so I'm in favour of the "ain't broke"
approach.  To work-around this, I have just put yum into the existing
list of packages to be cleaned up.  I have added a note to the yum
installer taking note of this behaviour for future reference.

Change-Id: I8bbdc07ccdb89a105b4fc70d5a215077c42fcd03

elements/ironic-agent/finalise.d/99-remove-extra-packages

@@ -9,18 +9,21 @@ set -o pipefail
 # TODO(lucasagomes): optimize the ramdisk for other OSs
 if [ $DISTRO_NAME = 'fedora' ] ; then
 
-    install-packages -e kernel-debug-devel gcc fedora-logos python3 rsync sudo pykickstart grubby make genisoimage tcpdump man-db policycoreutils kbd-misc plymouth cronie
-
+    _remove_yum=''
     if [ $DIB_RELEASE -ge 22 ]; then
-        # Remove yum, >= F22 defaults to dnf
-        dnf remove yum -y
-        # Remove package manager cache
-        dnf clean all
-    else
-        # Remove package manager cache
-        yum clean all
+        # if we are on F22, we can remove yum if there, because it has
+        # been superseeded by dnf
+        _remove_yum='yum'
     fi
 
+    install-packages -e kernel-debug-devel gcc fedora-logos \
+                    python3 rsync sudo pykickstart \
+                    grubby make genisoimage tcpdump \
+                    man-db policycoreutils kbd-misc \
+                    plymouth cronie ${_remove_yum}
+
+    ${YUM:-yum} clean all
+
     # Rebuilding the rpm database after removing packages will reduce
     # its size
     rpm --rebuilddb

elements/redhat-common/finalise.d/01-clean-old-kernels

@@ -6,6 +6,16 @@ fi
 set -eu
 set -o pipefail
 
-install-packages yum-utils
+YUM=${YUM:-yum}
 
-package-cleanup --oldkernels -y --count=1
+if [[ ${YUM} == "dnf" ]]; then
+    # cribbed from
+    #  http://dnf.readthedocs.org/en/latest/cli_vs_yum.html
+    _old_kernels="$(dnf repoquery --installonly --latest-limit -1 -q)"
+    if [[ -n "${_old_kernels}" ]]; then
+        dnf remove -y ${_old_kernels}
+    fi
+else
+    install-packages yum-utils
+    package-cleanup --oldkernels -y --count=1
+fi

elements/yum/bin/install-packages

@@ -122,6 +122,14 @@ if [ -n "$WHITELIST" ]; then
         exit 0
     fi
 
+    # yum & dnf have a feature/bug where missing packages in a list of
+    # packages for install/erase do not raise an error exit [1].
+    # There is a corner case when specifying just *one* package, where
+    # it will fail if the package is missing.  Thus install-packages
+    # follows this behaviour; we may need to re-evaluate this at some
+    # point.
+    #
+    # [1] https://bugzilla.redhat.com/show_bug.cgi?id=965567
     ${YUM} -v -y $ACTION $EXTRA_ARGS $PKGS
 
     if [ "$ACTION" == "install" ]; then