Summary:
With the use of tmpfs or ramfs, unit tests related to GetUniqueID()
failed because of the failure from ioctl, which doesn't work with these
fancy file systems at all.

I fixed this issue and make sure all related tests run on the "regular"
storage (disk or flash).

Test Plan: TEST_TMPDIR=/dev/shm make check -j32

Reviewers: igor, dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16593