vold: Honor mount options for ext4 mounts

Change-Id: Ie77e0d402c2c16d544251f7fdaeaad34d030d121
Validate asec names.

Make sure asec names only contain alphanumeric, underscores,
dots, or dashes. Don't allow double dots.

Bug: 12504045
Change-Id: I3dd0350c79327dc91a5a10d5724d85d99814e769