Multi-arch application installs.

Each application now has two ABIs, the primary
and the secondary. The app is always launched with
the primary, but the secondary might be used by other apps
that load the given applications code. This implies we
must:

- dex2oat the app both ways.
- extract shared libraries for both abis.

The former is relatively straightforward but the latter
requires us to change the layout for shared libs that we
unpack from applications. The bulk of this change deals
with the latter.

This change continues to fill in nativeLibraryPath during
scans for backwards compatibility. This will be removed in
a future patch.

Change-Id: Ia943dd11ef815c5cbfc60f17929eaa2a652a385a