ANDROID: Incremental fs: Fix four resource bugs

Without these, you can't unmount a volume on which incfs was
mounted and the tests run.

Also incfs_tests would fail sporadically without the fix to
test_inode

Test: Run incfs_test and unmount underlying volume 1000 times
Bug: 152636070
Signed-off-by: Paul Lawrence <paullawrence@google.com>
Change-Id: I88f11f5d4269c22d9073e5eb671d0c7cc4629f6c
(cherry picked from commit c062bc8e)