use Tempfile to create temp files, avoiding potential random conflicts
make safe_run return the command's output

if something needs to check whether the command failed or not, it
should rescue the exception that safe_run raises
add a get_tempdir method to Utils
Add Zookeeper 'database' class, for backing up zookeeper snapshots + txlogs
remember to delete the tempdir at exit
Merge pull request #12 from airbnb/zookeeper

Add Zookeeper 'database' class