build: ota: Support for install tools in /tmp/install

 * Anything in OUT/install gets packaged up into the zip and extracted
   to /tmp/install immediately after FullOTA_InstallBegin.

 * Use /tmp/install in edify scripts and remove code related to using
   and manipulating /system for install tools.

 * Modified to support signing steps being split from build steps.

   Package install files into target-files INSTALL path
   Read from target-files for OTA package creation

   From Change-Id: I64f919c2a757b5474f6cc5f82bd6c33c2a8b558a

Change-Id: I315a3238e36c8d15e26f935e272f7e27dd59c320