releasetools: Add ability to make bootzip squashed

Add ability to make flashble kernel zips squashed from slimroms

Initial Commit
https://github.com/SlimRoms/android_build/commit/7113ad0db7e174447cbaa5de7d8949d6a9c6f884

convert bash to python for the bootzip creator script
https://github.com/SlimRoms/android_build/commit/e250b0fb8157fec0931def8e4d2a74ac7ea422a1

boot_flash_from_image: Strip kernel modules
https://github.com/SlimRoms/android_build/commit/02f5ac2c60d8fc12c0fb12dd1a28d360f20eb250

Change-Id: I204b7f4a51dfa36f8ffb6209d33405cbb11faa6e