Migrate remaining modules to use get_bin_path in module_common.py

* 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.

library/apt_repository

@@ -48,8 +48,7 @@ def main():
 
     add_apt_repository = module.get_bin_path(ADD_APT_REPO)
     if add_apt_repository is None:
-        module.fail_json(msg='Unabled to find any of the following executables '
-                             '%s' % binaries)
+        module.fail_json(msg='Unable to find executable %s' % ADD_APT_REPO)
 
     repo = module.params['repo']
     state = module.params['state']