Use inode numbers for CE storage, fix sizes.

Certain operations, such as clearing/destroying app data, or just
counting on-disk size, require us to know the CE storage directory
of a particular app.  To facilitate these operations, offer a method
to get the inode of a CE directory, and accept that inode number
for later operations.

In previous releases, we started installing apps using a new
directory-based layout, where all app code, unpacked native libraries,
and optimized code is bundled together.  So now we only have a single
path to measure for code size.

Start measuring both CE and DE storage data usage for apps, and tweak
the reporting so that empty cache/data directories actually show up
as "0 bytes".

Fix bugs in disk usage counting, since st_blksize has no bearing on
the allocated disk space.  Also don't double-count "." and ".."
directories when measuring storage.

Bug: 27828915, 27197819
Change-Id: I350b951f5c24165edb253ac663c9aae020c24dc9