Try to encrypt /data/media/obb but ignore failures

Try to encrypt /data/media/obb but ignore failures

Bug: 64566063
Test: We test whether it's encrypted by trying to move a file from
/data/unencrypted into it. Used this test to make sure directory was
encrypted before change. Left file in directory, rebooted with change,
tested that it was still unencrypted. Deleted all files in directory,
rebooted again, tested that unencrypted files could no longer be moved
into directory.

Change-Id: I50df4949fb495ca8996c8a54e238af56a71f5df9