Execute action only if specified file using param removes exist (execute reverse control of creates).

Some usage eg.:

```yaml
- name: enable apache2 default websites
  action: command /usr/sbin/a2ensite $item
creates=/etc/apache2/sites-enabled/$item
  with_items:
    - default
    - default-ssl

- name: disable apache2 default websites
  action: command /usr/sbin/a2dissite $item
removes=/etc/apache2/sites-enabled/$item
  with_items:
    - default
    - default-ssl
```

This allows the use of ~ in the chdir argument of the command module
I know the later change is absolutely necessary as the first change
was not sufficient. It may be that the first change fixes shell and
the second fixes command.

Make pep8 tests run against the library directory as well, and associated tweaks (mostly to indentation) in the library
directory.

Teach the common module code to warn users about typo'd arguments and also set everything to None automatically such
that code doesn't have to do a lot of params.get('foo', None) everywhere.

the 'chdir' argument changes the current working directory to the
fullpath supplied as its value, before the execution of the command.

Port command module over to new common code.  Notice that this has to subclass AnsibleModule -- this should be the only
one that has to do that.

The ohai and facter modules use /usr/bin/logger to log the fact that
they have been invoked.  I added 'import os' to the ping module
so that it could have the same syslog statements as the other modules.
I separated the condensed:
    shlex.split(open(argfile, 'r').read())
into two separate statements similar to the other modules.

already exists

Fix async to use the new argfiles method (wrapping brain around rock, really must write module development guide)

may forget about -a.  The CLI already warns about no host pattern by pulling up usage.

Cleanup is due in runner.py

CentOS5 has python 2.4 which doesn't have a built-in json
module