releasetools: squash backuptool support

this is a squash of the following commits:

commit 30e43f85
Author: Chris Soyars <ctso@ctso.me>
Date:   Thu Dec 23 00:44:33 2010 +0100

    Add otapackage support for backuptool

    Change-Id: I512554c579d444067cd3ccbb0e6946a5eb6bc964a

    Modular backuptool.sh.  Executes backup and restore methods defined in arbitrary /system/addon.d/*.sh scripts.

    * Copy backuptool.functions alongside backuptool.sh.
    * Delete both from /system/bin as they are not useful there.

    Patch Series
    ============
    http://review.cyanogenmod.com/#change,13265
    CyanogenMod/android_build
      * edify generator
    http://review.cyanogenmod.com/#change,13266
    CyanogenMod/android_system_core
      * permissions on /system/addon.d
    http://review.cyanogenmod.com/#change,13267
    CyanogenMod/android_vendor_cm
      * 50-cm.sh reference backup script
      * modular backuptool.sh
      * support backuptool.functions used by /system/addon.d/*.sh scripts

    Change-Id: I26b4907d28f49c69627699d2accd2f0fa2d1b112

    update ota_from_target_files to handle mounting/unmounting for backupscript

    backupscript should not be mounting/unmounting itself as it makes other
    scripts have unexpected results (such as modelid_cfg, which expects /system
    to be mounted)

    instead have the ota script handle the mounting/unmounting

    Change-Id: I94511f4147c624d975cb3ecbeaa8b0e98f63437c

    build: Don't run backuptool on GMS builds

    Change-Id: I5dde27f9d16b88049171db9805221d92e67f3e5d

commit 66ce73d1
Author: Tom Marshall <tdm@cyngn.com>
Date:   Wed Apr 9 16:14:07 2014 -0700

    build: edify: use set_metadata for backuptool

    Also use saner permissions on backuptool.sh

    Change-Id: I50742b51867aa358f5924b8dc208833092a35bd9

commit dac6e8fee851433ff35723f2a790e3930aaeb113
Author: Ricardo Cerqueira <ricardo@cyngn.com>
Date:   Wed Nov 5 18:16:43 2014 +0000

    ota: Include copies of the recovery scripts even if shipping in block mode

commit 5a6d5b87d44f638307531f29c89d19b41c79532b
Author: Ricardo Cerqueira <ricardo@cyngn.com>
Date:   Wed Nov 5 19:58:59 2014 +0000

    ota: Fix recovery-script cleanups in block mode

    Change-Id: Iadb480f8062cfb7a0e6c9024e32ac0d71a7481d7

Change-Id: I2401d334d8e16d18d3770b339ec2c787dd8e477c