expanduser on each component of plug-in paths

ansible.constants was calling expanduser (by way of shell_expand_path)
on the entire configured value for the library and *_plugins
configuration values, but these values have always been interpreted as
multiple directories separated by os.pathsep.  Thus, if you supplied
multiple directories for one of these values, typically only the first
(at least on *nix) would have e.g. "~" expanded to HOME.

Now PluginLoader does expansion on each individual path in each of
these variables.

lib/ansible/utils/plugins.py

@@ -16,6 +16,7 @@
 # along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
 
 import os
+import os.path
 import sys
 import glob
 import imp
@@ -108,6 +109,7 @@ class PluginLoader(object):
         # look in any configured plugin paths, allow one level deep for subcategories 
         configured_paths = self.config.split(os.pathsep)
         for path in configured_paths:
+            path = os.path.expanduser(path)
             contents = glob.glob("%s/*" % path)
             for c in contents:
                 if os.path.isdir(c):