* We'll first check the currently loaded slot. We can
assume the user just flashed a rom and that the target
slot for this rom is the other slot, so mount that
system image. TODO: autodetect this somehow
* Mount this system partition at /system_root (rw) and then
mount the /system/system folder at /system. We do it
this way for a couple reasons. Because it makes the
script easier to work with and because we're using
toybox from the system partition for operations, which
is expecting /system/bin/linker64 to exist.
Change-Id: Ia6f96f0864d725b0123665bbbce0e31523bb834f
12914fac70