init: Sort the list of flattened APEX folders to avoid variations

 * In 'ActivateFlattenedApexesFrom', the 'readdir' detects
   the APEX folders in a random way that depends on filesystems,
   built packages and order of the build chain

 * In normal cases, this is not an issue, however when building
   with Go configurations, we have a case where the package
   'com.android.tethering.inprocess' is built along the
   'com.android.tethering' overriden binary, and depending on
   the 'readdir' output, the mounts break the Tethering service

Change-Id: I8ac4a0284d8d885f732c71e846933869cf16a0bd
Signed-off-by: Adrian DC <radian.dc@gmail.com>