make sure that cluster_name is a valid filename

[Stephenitis]

in cluster.yml

cluster_name: "coreos-flocker>"

ran into this error when I did not remove the <cluster_name> from the cluster_name

error message referenced confusing me.

/bin/sh: 1: Syntax error: end of file unexpected
main function encountered error
Traceback (most recent call last):
  File "/opt/flocker/bin/flocker-config", line 9, in <module>
    load_entry_point('UnofficialFlockerTools==0.5', 'console_scripts', 'flocker-config')()
  File "/opt/flocker/lib/python2.7/site-packages/unofficial_flocker_tools/config.py", line 147, in _main
    react(main, sys.argv[1:])
  File "/opt/flocker/lib/python2.7/site-packages/twisted/internet/task.py", line 875, in react
    finished = main(_reactor, *argv)
  File "/opt/flocker/lib/python2.7/site-packages/twisted/internet/defer.py", line 1253, in unwindGenerator
    return _inlineCallbacks(None, gen, Deferred())
--- <exception caught here> ---
  File "/opt/flocker/lib/python2.7/site-packages/twisted/internet/defer.py", line 1107, in _inlineCallbacks
    result = g.send(result)
  File "/opt/flocker/lib/python2.7/site-packages/unofficial_flocker_tools/config.py", line 21, in main
    c.run("flocker-ca initialize %s" % (c.config["cluster_name"],))
  File "/opt/flocker/lib/python2.7/site-packages/unofficial_flocker_tools/utils.py", line 208, in run
    result = subprocess.check_output(command, shell=True)
  File "/usr/lib/python2.7/subprocess.py", line 573, in check_output
    raise CalledProcessError(retcode, cmd, output=output)
subprocess.CalledProcessError: Command 'flocker-ca initialize <descriptive name>' returned non-zero exit status 2