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/user

@@ -36,12 +36,11 @@ if os.path.exists('/etc/master.passwd'):
 # That is, this won't work on FreeBSD.
 
 def get_bin_path(module, arg):
-    if os.path.exists('/usr/sbin/%s' % arg):
-        return '/usr/sbin/%s' % arg
-    elif os.path.exists('/sbin/%s' % arg):
-        return '/sbin/%s' % arg
-    else:
+    bin = module.get_bin_path(arg)
+    if bin is None:
         module.fail_json(msg="Cannot find %s" % arg)
+    else:
+        return bin
 
 def user_del(module, user, **kwargs):
     cmd = [get_bin_path(module, 'userdel')]