wic: use kernel_dir to find systemd-efi bootloader
Fixed test failure caused by using bootimg_dir path
instead of kernel_dir to find systemd-efi bootloader:
FAIL: test_systemd_bootdisk (oeqa.selftest.wic.Wic)
...
FileNotFoundError: [Errno 2] No such file or directory:
'tmp/work/qemux86_64-poky-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/share'
Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
