Added required as optional argument to get_bin_path(). It defaults to
false.  Updated following modules to use required=True when calling
get_bin_path():  apt_repository, easy_install, group, pip,
supervisorctl, and user.
Also removed _find_supervisorctl() from supervisorctl module and updated
_is_running() to not need it.

* Migraed easy_install, pip, service, setup, and user.
* Updated fail_json message in apt_repository
* Fixed easy_install to not hardcode location of virtualenv in
  /usr/local/bin/.
* Made handling of virtualenv more consistent between easy_install and
  pip.

Retrieve the pip path after creating a non-existent virtualenv.
Prevents the problem of using the wrong pip if virtualenv doesn't
exist yet.

pip failure message sometimes (always?) go to standard out. Return
both standard out and standard error when there's a failure.

Add module common code to allow it to be easier to indicate whether arguments are mutually exclusive, required in conjunction, or whether one of a list of arguments is required.  This simplifies writing Python modules.

The `val if something else something-else` syntax does not work prior to 2.5.

The `val if something else something-else` syntax does not work prior to 2.5