Add "-media" autofs map, to access data on removable media, such as CD
drives or flash keys.  It can be enabled by uncommenting a single entry
in default /etc/auto_master.  It can also be easily modified to use
fuse-based filesystems instead of in-kernel ones.

There is still one deficiency - the mountpoints are permanent, they
don't disappear when user removes the media.  Fixing it needs some
autofs changes.

Differential Revision:	https://reviews.freebsd.org/D1210
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation