Don't mount /tmp to /mnt/tmp. Fixes #3.

This reverts commit c3a31193f2f22c6f73725b0906c393f5eed85282. Though
mounting /tmp on the ephemeral partition was helpful for several of
our own background tasks, @mreinsch correctly points out that it's not
safe across platforms and layers. A separate custom cookbook should
handle this instead.
Bump version to 0.3