handle cron_file properly

In the cron module, if you specify a cron_file, the tmpfile gets moved and then the attempt to read it again (to get a list of all the jobs in it) fails:

        if changed:
            # If the file is empty - remove it
            if rm and cron_file:
                remove_job_file(cron_file)
            else:
                if backup:
                    module.backup_local(backupfile)
                (rc, out, err) = install_jobs(module,user,tmpfile.name, cron_file)            <-- file is moved here
                if (rc != 0):
                    module.fail_json(msg=err)
    
        # get the list of jobs in file
        jobnames = []
        for j in get_jobs(tmpfile.name):                    <--- tries to re-read the old location here
            jobnames.append(j[0])
        tmpfile.close()
    
        if not backup:
            os.unlink(backupfile)
            module.exit_json(changed=changed,jobs=jobnames)
        else:
            module.exit_json(changed=changed,jobs=jobnames,backup=backupfile)

An example of the error:

    TASK: [Add cron job for get-hyped] ********************************************
    <50.116.33.15> REMOTE_MODULE cron name=hyped job='ruby /opt/get-hyped/get-hyped.rb -d /opt/get-hyped/music -l /home/akerl/.hyped >/dev/null' cron_file=hyped minute=15 user=akerl
    fatal: [grego] => failed to parse: Traceback (most recent call last):
      File "/root/.ansible/tmp/ansible-1373506268.34-273775692436148/cron", line 1283, in <module>
        main()
      File "/root/.ansible/tmp/ansible-1373506268.34-273775692436148/cron", line 353, in main
        (rc, out, err) = install_jobs(module,user,tmpfile.name, cron_file)
    TypeError: 'NoneType' object is not iterable
    Exception OSError: (2, 'No such file or directory', '/tmp/tmpb26NJN') in <bound method _TemporaryFileWrapper.__del__ of <closed file '<fdopen>', mode 'w+b' at 0xeabb70>> ignored

This fixes it by copying rather than moving. As it's a tempfile, python cleans it up anyways when the script exits.