added main()

fix this traceback
```
[zenoss@1517d6cff529 ~]$ findposkeyerror
Traceback (most recent call last):
  File "/opt/zenoss/bin/findposkeyerror", line 9, in <module>
    load_entry_point('zenoss.toolbox==0.1.8', 'console_scripts', 'findposkeyerror')()
  File "/opt/zenoss/lib/python2.7/site-packages/pkg_resources.py", line 343, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/opt/zenoss/lib/python2.7/site-packages/pkg_resources.py", line 2309, in load_entry_point
    return ep.load()
  File "/opt/zenoss/lib/python2.7/site-packages/pkg_resources.py", line 2020, in load
    raise ImportError("%r has no %r attribute" % (entry,attr))
ImportError: <module 'zenoss.toolbox.findposkeyerror' from '/opt/zenoss/lib/python2.7/site-packages/zenoss/toolbox/findposkeyerror.py'> has no 'main' attribute

```