Change to use kernel not bzImage everywhere

Previously we hardcoded `bzImage` which is not used for all
use cases or architectures.

fix #1630

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

tools/mkimage-vmdk/make-vmdk

@@ -5,7 +5,7 @@ set -e
 mkdir -p /tmp/image
 cd /tmp/image
 
-# input is a tarball of vmlinuz64 and initrd.img on stdin
+# input is a tarball of kernel and initrd.img on stdin
 # output is a vmdk on stdout
 
 mkdir -p files
@@ -17,10 +17,10 @@ cd files
 [ -t 0 ] || tar xf -
 
 INITRD="$(find . -name '*.img')"
-KERNEL="$(find . -name vmlinuz64 -or -name '*bzImage')"
+KERNEL="$(find . -name kernel -or -name '*bzImage')"
 CMDLINE="$*"
 
-[ "$KERNEL" = "./vmlinuz64" ] || mv "$KERNEL" vmlinuz64
+[ "$KERNEL" = "./kernel" ] || mv "$KERNEL" vmlinuz64
 [ "$INITRD" = "./initrd.img" ] || mv "$INITRD" initrd.img
 
 # clean up subdirectories
@@ -28,7 +28,7 @@ find . -mindepth 1 -maxdepth 1 -type d | xargs rm -rf
 
 CFG="DEFAULT linux
 LABEL linux
-    KERNEL /vmlinuz64
+    KERNEL /kernel
     INITRD /initrd.img
     APPEND ${CMDLINE}
 "