Check if sdcard daemon exited.

Check if sdcard daemon exited.

If the system is using sdcardfs, the sdcard daemon exits after mounting.
If it's using FUSE, the sdcard daemon runs until we go to unmount.

Bug: 37638548
Test: Run "adb shell ps | grep -w Z" with sdcardfs enabled.
      The sdcard daemon should not be listed.
      Run again with sdcardfs disabled. The daemon should be
      running, and vold should not be stuck waiting on it.
Change-Id: I930d22b35194ec99e7a6a4a022a04d36f4f39a34