android/kernel/kernel_utils.c: Support probing version for ARM64 kernel images. The ARM64 kernel images are not compressed but contain a GZip header that appears _after_ the actual 'Linux version ' string. This patch modifies the probing code to handle this gracefully. + Update unit tests. Change-Id: Id486e9ba29c894bc6f7f863789f120c7c8ab22a0