Update kernel-install Plugin

- Update memtest86+.kernel-install-plugin to fallback to
   20-grub.install behaviour (RHBZ#2137395)

memtest86+.kernel-install-plugin

@@ -1,4 +1,8 @@
 #!/usr/bin/bash
+#
+# Manage memtest86+ install location and bootloader config.
+# Currently only manages GRUB with BLS support enabled.
+#
 
 # Sanity Checks
 if ! [[ $KERNEL_INSTALL_MACHINE_ID ]]; then
@@ -17,10 +21,16 @@ MEMTEST_VERSION="$2"
 BOOT_DIR_ABS="$3"
 MEMTEST_IMAGE="$4"
 
-IMAGE_DIR="${MEMTEST_IMAGE%/*}"
+MEMTEST_DIR="${MEMTEST_IMAGE%/*}"
 BOOT_ROOT="${KERNEL_INSTALL_BOOT_ROOT}"
 MACHINE_ID="${KERNEL_INSTALL_MACHINE_ID}"
 BLS_DIR="${BOOT_ROOT}/loader/entries"
+# Fail back to /boot default if BLS_DIR
+# doesn't exist already, matching 20-grub.install
+if [[ ! -d "${BLS_DIR}" ]]; then
+    BOOT_ROOT="/boot"
+    BLS_DIR="/boot/loader/entries"
+fi
 BLS_ENTRY="${BLS_DIR}/${MACHINE_ID}-0-memtest86+.conf"
 
 # Setup functions
@@ -38,7 +48,7 @@ grub_class ${ID}
 EOF
 }
 
-# If ${BOOT_DIR_ABS} exists, some other boot loader is active.
+# If ${BOOT_DIR_ABS} exists, non-grub boot loader is active.
 [[ -d "${BOOT_DIR_ABS}" ]] && exit 0
 
 case "$COMMAND" in