Simplify permitted-path construction

The white list of permitted directories is applied for every
classloader namespace by libnativeloader. LoadedApk no longer
needs to do that.

Add mDataDir to permitted paths in the case if for any reason
it is outside of the whitelisted dirs.

Bug: http://b/28639227
Change-Id: I5b61ac64e281ecee3e3e9b1fe56cf04dc6ee7b25