Fix readonly directories

Some directories might not have u+w originally, and tarfile will restore that. Then, putting a file in the directory will fail with "permission denied". We can just change the chmod on the directory when we copy.

b99d5e54 on v0.3 fixes #57, since copying busybox in the chroot folder is probably the only affected operation.

On master, other operations are probably affected. Operations happening as root shouldn't run into this problem (root is not subject to filesystem permissions).

Things to check:
* [X] Creating directory/chroot (others happen as root)
* [X] Uploading
* [x] Destroying directory/chroot