Raise error if zip or unzip fail

I ran into a case where it seemed to fetch the tarball from S3 correctly but it failed to extract:

```
$ travis_retry ~/wad
[wad] Trying to fetch Wad from S3
[wad] Unpacking Wad with tar (/home/travis/build/.../fc4466782de707bd80dff01f2fc59f7a.tar.bz2)
bzip2: Compressed file ends unexpectedly;
	perhaps it is corrupted?  *Possible* reason follows.
bzip2: Inappropriate ioctl for device
	Input file = (stdin), output file = (stdout)
It is possible that the compressed file(s) have become corrupted.
You can use the -tvv option to test integrity of such files.
You can use the `bzip2recover' program to attempt to recover
data from undamaged sections of corrupted files.
tar: Unexpected EOF in archive
tar: Unexpected EOF in archive
tar: Error is not recoverable: exiting now
[wad] Installing bundle
... 
```