vold: use blkid to detect filesystem type

In preparation for handling ext4 partitions via vold and fuse.

Change-Id: Ibaccded63a7a293ad53f16afb80448ddd493554c
vold: add support for ext4 media

Depends on:
http://review.cyanogenmod.org/31202
http://review.cyanogenmod.org/31211

Result:
http://pastebin.com/nzUbvW7K

Change-Id: I5bd227e637f2a1ed4d13a2eb81390c56c953f482