Attempting to build after a failed build fails

[keithcallenberg]

If you specify a bad coreos channel-version combination, it creates the bz2 file anyway, causing the following situation (beta 1409.5.0 does not exist, but stable 1409.5.0 does):

core@ip ~/coreos-nvidia-master $ ./build.sh 384.59 beta 1409.5.0
Keeping container around after build: false
Additional flags: 
Downloading CoreOS beta developer image 1409.5.0
Decompressing
bunzip2: coreos_developer_container.bin.1409.5.0.bz2 is not a bzip2 file.
Caught error
Cleaning up
Cleaning up
core@ip ~/coreos-nvidia-master $ ./build.sh 384.59 stable 1409.5.0
Keeping container around after build: false
Additional flags: 
Downloading CoreOS stable developer image 1409.5.0
Decompressing
bunzip2: coreos_developer_container.bin.1409.5.0.bz2 is not a bzip2 file.
Caught error
Cleaning up
Cleaning up

[keithcallenberg]

Workaround is to just delete the bad .bz2. But would be nice if cleanup caught this.