securelaunch: launcher: unmount kernel/initrd files if kexec fails.
securelaunch: launcher: unmount kernel/initrd files if kexec fails.

found a bug wherein in the case of kexec failure, devices holding
the kernel and initrd files were left mounted. This would prevent
sluinit from being run again manually on the console.
This change fixes this bug.

Signed-off-by: Simran Singh <83c3bfa9a00ecf3331cec3f1babab6589b76d543@oracle.com>

hugelgupf/u-root,hugelgupf/u-root,u-root/u-root,hugelgupf/u-root,u-root/u-root,hugelgupf/u-root,u-root/u-root