kernel-install: do not add kernel entry if already present

The entry may be already present for example when reinstalling package,
or calling the script multiple times (which apparently is the case
during system installation).

(cherry picked from commit 4d4e7cc5e9)

system-config/kernel-xen-efi.install

@@ -15,6 +15,7 @@ fi
 
 case "$COMMAND" in
     add)
+        if ! fgrep -q "[${KVER}]" $EFI_DIR/xen.cfg; then
             # take the default section and use it as a template for the new entry
             awk -F = --assign "kver=${KVER}" '
               /^\[/ {
@@ -57,6 +58,7 @@ case "$COMMAND" in
             
             # then change the default
             sed -e "s/default=.*/default=$KVER/" -i $EFI_DIR/xen.cfg
+        fi
 
         cp "/boot/vmlinuz-$KVER" "$EFI_DIR/"
         dracut -f "$EFI_DIR/initramfs-${KVER}.img" "$KVER"