earlykdump: add more sanity check when generating initramfs

Currently when earlykdump failed to install required kernel image or
initramfs, it will still install the earlykdump hook and other utils.
But it won't work due to the absent of kernel image or kdump initramfs,
so the hook and installed utils is meanless.

We can't simply fail dracut building, as if earlykdump is included by
dracut config file, this may fail kernel update, where kernel image is
installed but initramfs failed to generate, and then it will fail
booting.

So this patch let it skip earlydkump install if anything is missing and
give a clean error message to let the user better ware of the situation.

Signed-off-by: Kairui Song <kasong@redhat.com>
Acked-by: Dave Young <dyoung@redhat.com>

dracut-early-kdump-module-setup.sh

@@ -32,13 +32,25 @@ prepare_kernel_initrd() {
 }
 
 install() {
+    prepare_kernel_initrd
+    if [ ! -f "$KDUMP_KERNEL" ]; then
+        derror "Could not find required kernel for earlykdump," \
+            "earlykdump will not work!"
+        return 1
+    fi
+    if [ ! -f "$KDUMP_INITRD" ]; then
+        derror "Could not find required kdump initramfs for earlykdump," \
+            "please ensure kdump initramfs is generated first," \
+            "earlykdump will not work!"
+        return 1
+    fi
+
     inst_multiple tail find cut dirname hexdump
     inst_simple "/etc/sysconfig/kdump"
     inst_binary "/usr/sbin/kexec"
     inst_binary "/usr/bin/gawk" "/usr/bin/awk"
     inst_script "/lib/kdump/kdump-lib.sh" "/lib/kdump-lib.sh"
     inst_hook cmdline 00 "$moddir/early-kdump.sh"
-    prepare_kernel_initrd
     inst_binary "$KDUMP_KERNEL"
     inst_binary "$KDUMP_INITRD"