Don't build cache by default. Use BOARD_GENERATE_CACHEIMAGE to control it.

Change-Id: I5cee499a47d8cc1785634c4fdda126c2c57bdf80
Partially revert 8263ad86d4684ededd26113387c8b5a18799a036
Leave Aaron's commit part as it was

Change-Id: Ic3e79f55711822c306ab5801e5db89d7d7016a8c
Import OTA system:

Credit to Mokee

commit e24986aaaab4e3d28e597b1dcad3fc84133b0c60
Author: xilence2210 <xilence2210@gmail.com>
Date:   Fri Nov 8 11:24:42 2013 +0800

    OTA: import variable ANDROID_BUILD_TOP

    Change-Id: I7000752d9d01052865f055cfe3c0f132eac38404

commit 249330c5cd17c67df3a27ba499d26210c812a9aa
Author: xilence2210 <xilence2210@gmail.com>
Date:   Fri Oct 25 17:36:22 2013 +0800

    [Stage 1]OTA system (Build part)

        OTA system from Mokee

        port ota command to remixpa(ota_all cannot be used for now)
        still need to test

    Change-Id: Iec65015c09530c4252b1a344139aaa241bae360c

    Conflicts:
    	envsetup.sh

Change-Id: I2ab4377fe0f734de2a4c9ccbe6e63e3eadb31c37