Fix conflicts with system python modules

If python system module had a name that conflicted in some way
with a plugin, the plugin load would fail.  Fix this by prioritizing
the plugin path over system locations.  Also, to avoid the breakage
going the other way, remove the plugindir from the system path when
that particular directory is done.

confluent_server/confluent/core.py

@@ -78,7 +78,7 @@ def load_plugins():
         plugindir = os.path.join(plugintop, plugindir)
         if not os.path.isdir(plugindir):
             continue
-        sys.path.append(plugindir)
+        sys.path.insert(1, plugindir)
         # two passes, to avoid adding both py and pyc files
         for plugin in os.listdir(plugindir):
             if plugin.startswith('.'):
@@ -96,6 +96,8 @@ def load_plugins():
                     pluginmap[name] = tmpmod
             else:
                 pluginmap[plugin] = tmpmod
+        # restore path to not include the plugindir
+        sys.path.pop(1)
 
 
 rootcollections = ['noderange/', 'nodes/', 'nodegroups/', 'users/', 'events/']