Use canonical path for /vendor/app

It wasn't possible to start apps installed in /vendor/app
on a device where /vendor was a symbolic link to /system/vendor.
This is currently the default configuration for android (see
init.rc)

During installation a dex file is created at:
/data/dalvik-cache/vendor@app@blah.blah.apk@classes.dex

But dalvik would fail to start this app with the following error:
I/dalvikvm( 3453): Unable to open or create cache for /system/vendor/app/blah.apk \
(/data/dalvik-cache/system@vendor@app@blah.blah.apk@classes.dex)

Note that dalvik were trying to start /system/vendor/app while the
app was installed in /vendor. There was a conflict between the
package manager and dalvik on how to interpret paths. This change
makes the package manager consistent with dalvik.

Change-Id: I1c7e3c3ae45f97dd742cbf06f7965a7405c821a7