With native FBE, lock user directories when framework is started

If the framework is restarted, the user must unlock their device in the
same way as after a reboot.  But with FBE, vold was never told to lock
the credential-encrypted storage directories, so any that were unlocked
at the time the framework stopped remain unlocked, i.e. their keys are
still in the kernel.  This is unexpected and differs from a reboot.

Fix this by locking all user directories when the framework is started.
This was already done for emulated FBE, but this change extends it to
native FBE too.

Test: Unlock device with PIN.  Then in adb shell: 'stop; start;
      sleep 10; ls /data/data/' shows filenames in ciphertext form.
Change-Id: If993d93d9837b09ff8029642f8641dec69af04e0